Range Report Which Published Berger BCs Are From Predictions Rather than Measurements?

[Michael Courtney]

Which Published Berger BCs Are From Predictions Rather than Measurements?

Both Eric Stecker and Bryan Litz give the definite impression that Berger's BCs published since 2009 or so are the result of Bryan's careful and well documented BC measurement system (using an acoustic method over 600 yards) rather than the output from any kind of predictive model.

For example, in a blog post dated 30 January 2009, Eric Stecker wrote:

A few months ago Bryan became Berger Bullet’s full time Chief Ballistician. Since Bryan has the ability to accurately measure fired BCs with +/- 1% repeatability and since we are committed to providing shooters with the best product and data it was an obvious and simple decision to update our published BCs to Bryan’s fired numbers. (Why Our BC Numbers Have Changed (Been Corrected) | Berger Bullets Blog )

Bryan Litz has written:

The first thing I did when I started working for Berger was to reassess all the advertised BC’s (which were based on computer predictions) to the actual measurements I took from live fire and averaged over long range. This resulted in an average 3% to 5% reduction in Bergers [sic] advertised numbers. I also introduced the idea of using G7 BC’s [sic] to minimize velocity effects.

The effect of the claim to have measured ALL of Berger's advertised ballistic coefficients is to give customers the impression that the likely accuracy level corresponds to the 1% or so claimed accuracy of the Litz measurement system rather than much less accurate predictive models, such as the McDrag model developed by Bob McCoy at BRL or the Litz predictive model published as equation 17.1 in his 2009 book, Applied Ballistics for Long Range Shooting.

The attached figure shows changes in Berger's advertised ballistic coefficients between 20 October 2008 (when Berger was using a predictive model attributed to Bill Davis for their BCs) and 14 April 2010 (after Berger had purportedly updated their advertised BCs to "Bryan's fired numbers" (to quote Eric Stecker). In total (counting bullets with the same shape and BC only once), the BCs of 66 bullets were updated, and the percent differences in these new BCs are shown as red squares in the graph. However, comparing with Bryan's book, Applied Ballistics for Long Range Shooting (the blue Xs) shows only 35 of the new BCs can be attributed to Bryan's experimental measurements.

Where did the new BCs for the other 31 bullets come from? The most plausible explanation seems to be that Berger re-calculated these BCs based on an "improved" predictive model (or a similar predictive model) based on equation 17.1 of Bryan's 2009 book. This model purports to have a 95% confidence level of 4.2% for boat tail bullets, but predictions for flat base bullets would likely be much less accurate.

One reason I lean toward this possibility is because the 115 grain .257 VLD had its BC advertised at 0.479 at the Berger site on 6 February 2009, and I received two boxes of these bullets with this BC printed on them at about that time. However, in Bryan's 2009 book and later on the Berger site, the BC was revised to 0.466. When I asked him about these differences, Bryan explained that the BC value of 0.479 had been based on a predictive model and used temporarily until the BC could actually be measured with his method. I think several other bullets (like the 87 grain .257 bullet) whose advertised BCs were changed twice between 10/26/2008 and 2/6/2009 and 4/14/2010 may have also had the intermediate value based on a predictive model later changed to a model based on measurement. It is certainly possible that all 66 bullets were updated based on actual measured BCs, but it is also possible that some bullet BCs were updated based on a predictive model and have still not been updated based on real measurement results.

It may be notable that while most of the bullets whose revised BCs seem to be based on a predictive model have BC adjustments under 5%, 16 of the 35 or 36 bullets that seem to be based in actual firing measurements have been adjusted downward by over 5%. Other than a 17 cal bullet, the biggest downward adjustments were the 87 grain .257 (-15.85%), the 115 grain .257 (-10.9%), and the 105 grain .243 VLD (-11.33%).

Now this may seem like so much ancient history, except that, for the bullets still in the Berger catalog, nearly all of the 30-31 bullets whose revised BC seems more likely based on a predictive model than actual firing measurements have had their advertised BCs unchanged since 14 April 2010.

In light of these concerns, I think Berger owes the shooting community some quick and honest answers regarding which of their currently advertised BCs have actually been measured by live firing and which are attributable to a less accurate predictive model. After all, Eric Stecker is on record as saying:

A BC is not a marketing tool and should not be inflated (intentionally or by using inaccurate means to calculate BC) for the purposes of selling more bullets. Some will say that inflating BC is smart business but frankly, we do not agree. A BC is an important number with physical meaning that’s used to calculate the trajectory of a given bullet which enables shooters to reliably engage targets at long range. The BC should allow a shooter to hit their aim point each and every time. There are many factors that influence the location of bullet impact but an accurate BC number is an essential component in achieving the most successful shooting experience no matter which brand you shoot. The bullet makers owe it to the shooters to provide them with truly accurate information about the performance of their product and that’s what we’re committed to.

When Berger was asked directly in 2014 whether the BCs of two specific varmint bullets had been measured directly or resulted from a predictive model, Eric Stecker hinted but dod not answer directly:

I won't say that we don't have a few FB bullets that need closer review but the varmint bullets are not our priority. Anything with a BT has been thoughroly tested.

Links to past Berger BC specs:


Berger Bullets - All Bullets

Berger Bullets - All Bullets

Berger Bullets

 

[TimeWillTell]

The only thing I can say about this is that in the applied ballistics software some bullets have (Litz) next to them. I believe these are the ones he actually tested (so far). Also, in his book he has many BCs that he actually tested not only from Berger but many manufacturers. If you don't have his book, its worth getting IMHO. Go to the back and he has a page per bullet of all important data from BC to drag curve to even the bullet measurements (even these measurements can vary from lot to lot, so don't get all worked up if its 0.005 off). I am sure this was a time consuming and costly endeavor. EVERY companies BCs are wrong in my experience to a certain degree, not a problem unique to Berger. Using a model that predicts your bullets BC on the HIGH end is something companies do to market their bullet.

There are a couple different .257 155gr VLDs listed in the AB software but one has (Litz) next too it and the G1 BC is listed as .466 which is not a >5% reduction as you seem to believe it should be but its less than the 0.479 you mention, regardless. I am also a big fan of the G7 model though and rarely ever use the G1 BC.

Personally I am grateful to Bryan for doing all this testing even though it may not be exhaustive. I hope he continues to do this testing and continues to branch out and measure other manufacturers bullets also. This allows the shooter to accurately compare between bullets of multiple manufacturers to determine what is best for them and is something the lay-person could never accomplish. The cost associated with accurate measuring all BCs in real world conditions is probably outrageous and it certainly isn't easy... Even with his measured BCs, it is probably still good practice to verify the BC using your rifle and your conditions are extended ranges.

Take this opinion for what you paid for it....

ETA: I missed the paragraph where you note the reduced BC to 0.466, sorry. My other opinions still stand that I feel Berger may be the most forthcoming bullet manufacturer when it comes to BC numbers. Stirring the pot over not having measured BCs for less popular bullets won't help.

 

[LastShot300]

Very interesting and I'm too waiting for the final answer. Thanks for getting our attention to this matter.

 

[gstaylorg]

Anyone reading this thread that wishes to get a better idea of where the OP is coming from should also look through the following threads:

Which Published Berger BCs Are From Predictions Rather than Measurements?


http://www.longrangehunting.com/for...-predictions-rather-than-measurements-140212/

 

[KYpatriot]

Well, first of all Berger doesn't "owe" anyone anything. They make excellent bullets that are accurate and have fantastic long range performance. I'd be pleased with them for that fact alone. Bryan's exhaustive efforts to nail down precise BCs for their most popular match and long range bullets are just icing on the cake and good customer service which I appreciate. I'd say you'd be better off asking them nicely if they would consider doing the same for the varmint series or measure them yourself. They have already done more than other manufacturers have in this regard. If people go yanking their chain, demanding more accurate BCs than the estimates they put on the box, they may not even give you that.

 

[TimeWillTell]

Well, first of all Berger doesn't "owe" anyone anything. They make excellent bullets that are accurate and have fantastic long range performance. I'd be pleased with them for that fact alone. Bryan's exhaustive efforts to nail down precise BCs for their most popular match and long range bullets are just icing on the cake and good customer service which I appreciate. I'd say you'd be better off asking them nicely if they would consider doing the same for the varmint series or measure them yourself. They have already done more than other manufacturers have in this regard. If people go yanking their chain, demanding more accurate BCs than the estimates they put on the box, they may not even give you that.

Yeah that's what I tried to say. Agree 100%.

 

[Michael Courtney]

Well, first of all Berger doesn't "owe" anyone anything. They make excellent bullets that are accurate and have fantastic long range performance. I'd be pleased with them for that fact alone. Bryan's exhaustive efforts to nail down precise BCs for their most popular match and long range bullets are just icing on the cake and good customer service which I appreciate.

Berger's web site is claiming (as of 8/29/14) that the BCs of the varmint bullets are measured and that the measurements are accurate to 1%, as the attached screen shot and text from clicking on the BC ? button shows.

The BC's of Berger bullets are based on carefully controlled test firing. The BC's established by this method are accurate to within +/- 1%, whereas BC's predicted by computer programs can have as much as +/- 10% error.

Now, I don't know where you come from, but where I come from, when a company makes a claim in the process of selling something to customers, they owe it to their customers to make good on that claim.

Or is your version of America a place where companies can lie to customers, and customers have no right to ask for the promised information?

 

[TimeWillTell]

I'm sure there are other companies that would be happy to have your business. Then you can start a thread when their BCs done match up with real world numbers. You may be typing a lot of these threads....

 

[Michael Courtney]

I'm sure there are other companies that would be happy to have your business. Then you can start a thread when their BCs done match up with real world numbers. You may be typing a lot of these threads....

We've already published papers pointing out the BC inaccuracies in bullets from Nosler (the worst offender), ATK, Federal, Speer, Barnes, and Hornady's lead tipped bullets. Barnes has improved greatly since they put in their 300 yard ballistics lab a few years ago, so they are more accurate on their newer releases.

We've done real well with the Hornady AMAX and VMAX bullets meeting their published BC specs. Other independent parties have also verified the accuracy of these BCs. Some BCs are slightly off (5% or so), but nothing like the 10-15% discrepancies we see in some of the Bergers. Great long range accuracy and terminal performance at the lower impact velocities. We've tested the 208 AMAX in ballistic gelatin down to subsonic velocities. When it drops below the expansion threshold, it tumbles reliably, and a tumbling bullet that long creates a tremendous wound channel. With a G7 BC of 0.324 and great terminal performance all the way down to 1100 fps, this bullet is a good performer. Another thing we really like about the Hornady plastic tipped bullets is that their BCs show excellent shot-to-shot consistency. Open tipped match bullets have inconsistent meplats which add a few percent to the shot to shot BC variations, so even if the average BC is higher than the AMAX, it's less consistent.

There are good reasons why two of the longest sniper kills ever were with Hornady AMAX bullets. How many of the top ten does Berger have?

We've just begun working with Lapua bullets, but all indications are that their BC numbers are accurate. Lapua has a few kills in the top ten also, with a G7 BC of 0.310 or so. Lapua's meplats tend to be more consistent than the most popular American open tipped bullets.

 

[TimeWillTell]

We've already published papers pointing out the BC inaccuracies in bullets from Nosler (the worst offender), ATK, Federal, Speer, Barnes, and Hornady's lead tipped bullets. Barnes has improved greatly since they put in their 300 yard ballistics lab a few years ago, so they are more accurate on their newer releases.

We've done real well with the Hornady AMAX and VMAX bullets meeting their published BC specs. Other independent parties have also verified the accuracy of these BCs. Some BCs are slightly off (5% or so), but nothing like the 10-15% discrepancies we see in some of the Bergers. Great long range accuracy and terminal performance at the lower impact velocities. We've tested the 208 AMAX in ballistic gelatin down to subsonic velocities. When it drops below the expansion threshold, it tumbles reliably, and a tumbling bullet that long creates a tremendous wound channel. With a G7 BC of 0.324 and great terminal performance all the way down to 1100 fps, this bullet is a good performer. Another thing we really like about the Hornady plastic tipped bullets is that their BCs show excellent shot-to-shot consistency. Open tipped match bullets have inconsistent meplats which add a few percent to the shot to shot BC variations, so even if the average BC is higher than the AMAX, it's less consistent.

There are good reasons why two of the longest sniper kills ever were with Hornady AMAX bullets. How many of the top ten does Berger have?

We've just begun working with Lapua bullets, but all indications are that their BC numbers are accurate. Lapua has a few kills in the top ten also, with a G7 BC of 0.310 or so. Lapua's meplats tend to be more consistent than the most popular American open tipped bullets.

When you say "we have published" who is "we?" Just curious as I'm trying to figure out your background and intentions with this thread...

This is something that interests me greatly. Not the certain manufacturers and their BC specs specifically but just more along the lines of exterior ballistics in general.

 

[Michael Courtney]

When you say "we have published" who is "we?" Just curious as I'm trying to figure out your background and intentions with this thread...

This is something that interests me greatly. Not the certain manufacturers and their BC specs specifically but just more along the lines of exterior ballistics in general.

"We" in this context is my colleagues and co-authors. I'm a scientist who has probably co-authored more papers in ballistics than any other American in the 21st century. I've worked with co-authors at numerous government institutions and universities. I've also co-authored two papers with Don Miller, improving and updating his original stability formula for plastic tipped bullets. We'll have a few more papers out by the end of 2014, but here's a list of publications that is pretty close to complete right now:

Publications in External Ballistics

Michael Courtney and Amy Courtney, “Using Sound of Target Impact for Acoustic Reconstructions of Shooting Events,” Medicine, Science, and the Law, April 2012.

Michael Courtney, “Acoustic methods for measuring bullet velocity,” Applied Acoustics, October 2008.

Elya Courtney and Michael Courtney, “Gyroscopic Stability of Open Tipped Match Style Rifle Bullets,” General Physics, Cornell University Library, January 2014.

Elya Courtney and Michael Courtney, “Aerodynamic Drag and Gyroscopic Stability,” General Physics, Cornell University Library, August 2013.

Elya Courtney, Amy Courtney, and Michael Courtney, “Do Bullets Go to Sleep?” Long Range Hunting, March 2013.

Elya Courtney, Amy Courtney, and Michael Courtney, “Detecting Pitch and Yaw and In-flight Damping with Optical Chronographs” DTIC, November 2012.

Michael Courtney and Don Miller, “A Stability Formula for Plastic-Tipped Bullets,” Precision Shooting, January and February 2012.

Emily Bohnenkamp, Maurice Motley, and Michael Courtney, “Does Polishing a Rifle Bore Reduce Bullet Drag?” Precision Shooting, April 2011.

Emily Bohnenkamp, Bradford Hackert, Maurice Motley, and Michael Courtney, “Comparing Advertised Ballistic Coefficients with Independent Measurements,” DTIC, 2012.

Alex Halloran, Colton Huntsman, Chad Demers, and Michael Courtney, “More Inaccurate Specifications of Ballistic Coefficients,” DTIC, 2012.

Lionel Magee, Aaron Oats, and Michael Courtney, “Comparing Measured Bullet Weight with Manufacturer Specifications,” DTIC, 2012.

Michael Courtney and Amy Courtney, “An Acoustic Method for Determining Ballistic Coefficients,” Popular Physics, Cornell University Library, May 2007.

Michael Courtney and Amy Courtney, “The Truth about Ballistic Coefficients,” Popular Physics, Cornell University Library, May 2007.

Michael Courtney and Brian Edwards, “Measuring Bullet Velocity with a PC Soundcard,” Physics Education, Cornell University Library, January 2006.

Publications in Terminal Ballistics

Joe Caudell, Michael Courtney, and Clinton Turnage, “Evaluating Subsonic .308 Ammunition for Use in Wildlife Damage Management,” Proceedings of the 15th Wildlife Damage Management Conference, Clemson, SC, 2013.

Michael Courtney and Amy Courtney, “History and Evidence Regarding Hydrostatic Shock,” Neurosurgery, February 2011.

Michael Courtney and Amy Courtney, “Comments on 'Ballistics: A Primer for the Surgeon',” Injury, March 2008.

Michael Courtney and Amy Courtney, “Apparent measurement errors in 'Development of biomechanical response corridors in the thorax to blunt ballistic impacts',” Journal of Biomechanics, February 2008.

Amy Courtney and Michael Courtney, “Links between traumatic brain injury and ballistic pressure waves originating in the thoracic cavity and extremities,” Brain Injury, June 2007.

Steven Gaylord, Robert Blair, Amy Courtney and Michael Courtney, “Bullet Retarding Forces in Ballistic Gelatin by Analysis of High Speed Video,” DTIC, November 2012.

Amy Courtney and Michael Courtney, “Physical Mechanisms of Soft Tissue Injury from Penetrating Ballistic Injury,” DTIC, November 2012.

Maggie Sherrill, Rachel Bradley-Powers, Michael Courtney, and Amy Courtney, “Relative Armor Penetration of Jacketed Lead, Solid Copper, Solid Brass, and Steel Core Bullets,” DTIC, November 2012.

Christine Haight, Kadie McNamara, and Michael Courtney, “Does V50 Depend on Armor Mass?” DTIC, May 2012.

Amy Courtney and Michael Courtney, “Cerebrovascular injury caused by a high strain rate insult in the thorax,” Medical Physics, Cornell University Library, May 2011.

Michael Courtney and Amy Courtney, “Misleading reference to unpublished wound ballistics data regarding distant injuries,” Medical Physics, Cornell University Library, December 2008.

Michael Courtney and Amy Courtney, “The Ballistic Pressure Wave Theory of Handgun Bullet Incapacitation,” Medical Physics, Cornell University Library, March 2008.

Michael Courtney and Amy Courtney, “Scientific Evidence for Hydrostatic Shock,” Medical Physics, Cornell University Library, March 2008. Also DTIC 2010.

Michael Courtney and Amy Courtney, “A Method for Testing Handgun Bullets in Deer,” Medical Physics, Cornell University Library, February 2007.


Michael Courtney and Amy Courtney, “Review of criticisms of ballistic pressure wave experiments, the Strasbourg goat tests, and the Marshall and Sanow data,” Medical Physics, Cornell University Library, January 2007.

Michael Courtney and Amy Courtney, “Ballistic pressure wave contributions to rapid incapacitation in the Strasbourg goat tests,” Medical Physics, Cornell University Library, January 2007.

Michael Courtney and Amy Courtney, “Relative incapacitation contributions of pressure wave and wound channel in the Marshall and Sanow data set,” Medical Physics, Cornell University Library, January 2007.

Publications in Internal Ballistics

Elijah Courtney and Michael Courtney, “Studying the Internal Ballistics of a Combustion-Driven Potato Cannon using High-speed Video,” European Journal of Physics, July 2013.

Elya Courtney and Michael Courtney, “Powder Lot Variations: A Case Study with H4831 – Hodgdon Extreme,” Target Shooter, January 2013. Also DTIC November 2012.

Patrick Boyle, Alexander Humphrey, and Michael Courtney, “Quantifying Friction Effects of Molybdenum Disulfide, Tungsten Disulfide, Hexagonal Boron Nitride, and Lubalox as Bullet Coatings,” DTIC, July 2012.

Patrick Boyle, Alexander Humphrey, and Michael Courtney, “Friction Effects of Common Bullet Coatings in 5.56mm NATO,” Precision Shooting, August 2012.

Patrick Boyle, Alexander Humphrey, Spencer Proctor, and Michael Courtney, “Measuring Barrel Friction in the 5.56mm NATO,” DTIC, January 2012.

Amy Courtney and Michael Courtney, “Comparing Blast Pressure Variations of Lead Styphnate Based and Diazodintrophenol Based Primers,” Weapons Systems Technology Information Analysis Center Journal, October 2011.

Michael Courtney and Amy Courtney, “High Speed Measurements of Rifle Primer Blast Waves,” Precision Shooting, February 2011.

Michael Courtney and Amy Courtney, “A Method for Testing Bullets at Reduced Velocity,” Medical Physics, Cornell University Library, December 2008.

 

[KYpatriot]

Good. Then test those bullets, and write a book with good BCs in it like Bryan did and it will be well received.

Oh by the way, in "my version of America" smart asses get their co authored papers shoved up their ass.

 

[Michael Courtney]

Good. Then test those bullets, and write a book with good BCs in it like Bryan did and it will be well received.

Many parties that express confidence in BCs published by one party over others fail to appreciate important subtleties in the way BCs are experimentally determined and the velocity ranges over which validity and accuracy are claimed. The attached figure is useful for discussion.

The red Xs in the figure are drag coefficient measurements taken from Bryan's book, "Applied Ballistics for Long Range Shooting." The blue squares are our original measurements over a much wider range of Mach numbers. Bryan's measurements represent 2-4 shots and a range from M2.25 to M2.52 or so. Our measurements represent 80 shots from M1.36 to M2.97. Each blue point is the mean of the Cds at a given Mach number, with 10-20 shots at each Mach number. In most cases, the error bars are less than 1% and covered by the data point itself.

No one should lose any sleep over the small vertical displacement between Bryan's data and ours given that the experiments were performed with different rifles, different twist rates, different boxes of bullets, different measurement systems under different atmospheric conditions. That the two data sets are so close is a testament to the care taken in both experiments.

The real issue is that Bryan claims in his book that his data over such a small range of Mach numbers is sufficient to accurately determine ballistic coefficients from 1500 fps (M1.34) to 3000 fps (M2.68). Since our original Cd data actually spans M1.36 to M2.97, we could easily compute G1 and G7 BCs over that range. At Mach numbers where the uncertainty in the Cd is 1%, the corresponding uncertainty in BC will also be 1%. Except for M2.05 (close to 2%), most of our uncertainties are close to 1%. However, it would be a significant mistake to extrapolate our data and claim to have determined similarly accurate Cds or BCs at Mach numbers below M1.36 or above M2.97. It is without doubt that our paper would not have passed peer review had we done this.

Likewise, there is very little reason to assign validity to Bryan's published BCs that are well outside of the range of Mach numbers where the drag coefficients were actually measured. In this case, accuracy is ascribed to the published BCs from 1500 fps (M1.34) to 3000 fps (M2.68) in a case where measurements were made from M2.25 to M2.52. Careful review of the data on pp. 332-521 of Litz (2009) shows that in the majority of cases, the actual range of Cd measurements is much narrower than the M1.34 to M2.68 range for which BCs are presented that are purported to be accurate.

This is not to say that these measurements are without value, but rather that some have ascribed overly optimistic levels of accuracy and validity. A BC determined over a limited range of Mach numbers is still much more valuable than BCs determined by model predictions with no measurements at all.

 

[MontanaMarine]

MC, you seem to be on a mission to discredit Berger and Litz, on a few forums.

Berger/Litz have gone to great length, to provide detailed information on their bullets. That fact is well recognized among most practitioners of long range riflery.

Of course there will always be variations, heck even rifling style and twist rate probably affect BC to some degree. Then there is erector gearing. We will always need to 'prove' our rifle/ammo/scope.

If you have your own data to present, you should just do so, along with your supporting methods. If your information is good, it will always be well received, and appreciated.

 

[LastShot300]

MC, your work really interests me and I can certainly appreciate, given your scientific background, your concerns about the Mach range validity, something that always bothered me when it comes to high Mach testing ONLY. Do you have some link where I could download your papers? Thanks in advance for all of great work and insight, and please keep on it!

 

[Michael Courtney]

MC, your work really interests me and I can certainly appreciate, given your scientific background, your concerns about the Mach range validity, something that always bothered me when it comes to high Mach testing ONLY. Do you have some link where I could download your papers? Thanks in advance for all of great work and insight, and please keep on it!

Thanks for the encouragement.

The above list of our ballistics papers is fairly complete. Unfortunately, they are spread out in different places on the web and in print.

If you cut and past a title into Google, usually a link to the pdf will be very near the top.

If that fails, email me at [email protected] and I'll usually reply within a day with either a link or an attached pdf of the requested paper.

 

[mil_coder]

Michael - can you provide your published BC's for the following bullets? I'd like to run some analysis over here with them.

1) Berger 175 gr OTM
2) Sierra 175 gr MatchKing

-Nick

 

[Michael Courtney]

Michael - can you provide your published BC's for the following bullets? I'd like to run some analysis over here with them.

1) Berger 175 gr OTM
2) Sierra 175 gr MatchKing

-Nick

Nick,

Thanks for this request. I'm sorry if I gave the mistaken impression that we've published BCs for an exhaustive list of current bullet offerings.

We measure a lot of bullet BCs in the course of our laboratory work, and occasionally we publish papers with some tables of measured BCs of most of our measurement results. But we have not really endeavored to systematically measure BCs of most product offerings.

Sierra makes both 30 caliber and 7mm Matchkings in 175 grains. We have not measured BCs of either, but in general, I have confidence in Sierra's published BCs (with a couple of exceptions). If anything, perhaps Sierra may be overly conservative in some cases and the BCs may be higher than advertised. Sierra has all their BCs listed at their web site, and I have confidence that they have actually measured all their advertised BCs.

Berger has several 175 grain bullets, but none that I recall with OTM as part of the name. A quick review of our published material does not turn up any original BC measurements on 175 grain Bergers.

Best regards to you in your shooting endeavors!

 

[Christopher Rance]

Berger has OTM bullets. 175 gr OTM tactical is one of many. Link provided.
http://www.bergerbullets.com/products/tactical-bullets/

In regards to Sierra, they list their 175 SMK with a G1 BC of .496. In reality that BC is a .475 G1. I would say that's a pretty big difference if you ask me.

 

[JMGlasgow]

As Lowlight explained on other threads, G1 BC's rely heavily on velocity. So an advertised BC of .496 was calculated at a specific velocity. What was the velocity tested? I don't know the answer. The manufacturer may be able to explain better how the tests are conducted.

 

[Michael Courtney]

As Lowlight explained on other threads, G1 BC's rely heavily on velocity. So an advertised BC of .496 was calculated at a specific velocity. What was the velocity tested? I don't know the answer. The manufacturer may be able to explain better how the tests are conducted.

Sierra measures and publishes velocity dependent G1 BCs for their bullets.

Sierra's measured G1 BCs for the 175 grain .308 SMK are:

.505 @ 2800 fps and above
.496 between 1800 and 2800 fps
.485 @ 1800 fps and below

 

[mil_coder]

Berger has OTM bullets. 175 gr OTM tactical is one of many. Link provided.
http://www.bergerbullets.com/products/tactical-bullets/

In regards to Sierra, they list their 175 SMK with a G1 BC of .496. In reality that BC is a .475 G1. I would say that's a pretty big difference if you ask me.

Yeah Chris - 0.475 is definitely the right G1 BC for the average over the entire supersonic range. We've got a million rounds down range or so with that BC at our training facility and that's what we have all the guys run with. Any mismatch beyond the supersonic range is due to the usage of the G1 standard for modeling the 175 gr SMK.

 

[Michael Courtney]

Yeah Chris - 0.475 is definitely the right G1 BC for the average over the entire supersonic range. We've got a million rounds down range or so with that BC at our training facility and that's what we have all the guys run with. Any mismatch beyond the supersonic range is due to the usage of the G1 standard for modeling the 175 gr SMK.

What are the upper and lower velocities you consider for the "entire supersonic range"? Are you calling everything down to M1.0 "supersonic", or are you calling stuff below M1.2 or 1.5 "transonic"? Has anyone actually measured the BC (or drag coefficients) below M1.5, or are you inferring that the "average" BC across the whole range is correct simply because the bullets are hitting the right location?

We've got the ability to actually measure those BCs (or drag coefficients) all the way down to M1.0. I'm not aware of any actual published measurements below M1.5.

 

[stranded]

Michael, I have read and re-read this thread. Is your purpose to get Berger to hire you for BC testing of their products? I really don't understand where you are coming from. If you have the ability to measure BC's do so, then shoot!

 

[mil_coder]

What are the upper and lower velocities you consider for the "entire supersonic range"? Are you calling everything down to M1.0 "supersonic", or are you calling stuff below M1.2 or 1.5 "transonic"? Has anyone actually measured the BC (or drag coefficients) below M1.5, or are you inferring that the "average" BC across the whole range is correct simply because the bullets are hitting the right location?

We've got the ability to actually measure those BCs (or drag coefficients) all the way down to M1.0. I'm not aware of any actual published measurements below M1.5.

Here's the really cool part about the work we've been doing for the past several years is that we've measured not just drop, but drift as well. Our goal has always been to create an optical downrange crosswind sensor for small arms fire control systems. In order to do that, we needed to create an array of anemometers that could report the wind speed back to us at a centralized location. We created a test bed that allowed us to record the wind speed downrange at several positions as well as the time of the shot, atmospheric data, muzzle velocity, etc.

For obvious military reasons, we used the 175 gr SMK as our bullet of choice for testing not only the optical wind measurement system but the anemometers as well. For each shot not only did we record all of the aforementioned data, but we also recorded the drop and drift. We would aim at a central point on a large target board and let the bullet drift accordingly. For each shot, we measured both vertical deflection (from our center point) and horizontal drift. Shots were done at ranges between 800 and 1000 meters. For most of our data collection events, we were testing DA's between 1000 and 3000 feet.

After doing this for 1000's of shots, there are a number of interesting things that we saw with this round. If you plot the average crosswind speed sampled from the anemometers versus the bullet deflection, what you see is that for the 175 gr SMK at 950 meters (right around where the bullet was hitting Mach 1.0 most of the time) is that the deflection is approximately 0.9 meters of deflection per 1 meter per second of wind. That's from the empirical data. If you do it from Sierra's published BC's and run a modified point mass solver that can accept banded BC's, accounts for spin/coriolis/etc, then what you get is somewhere closer to 0.7 meters of deflection per 1 meter per second of wind. If you use 0.475 as the BC, you get somewhere closer to 0.8.

Since we didn't have BC data for the Sierra's between Mach 1.5 to Mach 1.0, we did our best to get the data to match up over large data sets. What we saw is that for ranges up to 800 (usually around Mach 1.2) is that our average BC over the entire flight of 0.475 worked well for drop and drift. We then used about 0.460 from 800 to 950-1000 meters (about Mach 1.2 to Mach 1.0) and then the drift matched up fairly well, showing the trends that we would expect to see that matched up with the empirical data.

Not unexpectedly, the drop then also matched up well also when we used the following bands:

Mach 3.0 - Mach 1.2 = 0.475
Mach 1.2 - Mach 1.0 = 0.460

All-in-all, it was super interesting data and those are the BC's we've been having the guys use in training. We've been doing this for other rounds as well for our optical crosswind work. The 175 gr SMK was a great starting point since it is so prolific.

If you have the ability to measure those BC's or the coefficient of drag as a function of Mach, I'd definitely be interested in the data and I can re-run the entire collection of data through post-processing on your numbers. I can accept either banded BC's or a custom drag curve with Mach/Cd data.

 

[Michael Courtney]

If you have the ability to measure those BC's or the coefficient of drag as a function of Mach, I'd definitely be interested in the data and I can re-run the entire collection of data through post-processing on your numbers. I can accept either banded BC's or a custom drag curve with Mach/Cd data.

I'll have my peeps look into ordering components and we'll start considering when we can get this scheduled. Please send me an email at [email protected] and I'll keep you know how things are proceeding. We can't post results online, but with minimal confirmation that you are in the US, we can email them to you. Our fall schedule is fairly packed, but the winter looks good.

 

[Lowlight]

Much of this discussion came up at the GAP Grind this past weekend. Including several .mil shooters, so it's actually quite timely.

In my personal experience, even today I find .496 to work better. ( though i like and use Sierras banded numbers most of the time, as listed above ) I think the "modified" part when talking about Point Mass is being purposely unkind to any original G1 value. And regardless of the G value used (G7 or G1) it was the general consensus that while the drops are very good in most of the current Point Mass solvers used, (everyone you talk to praises the drop) the windage is no where close to correct. I know I have been running multiple programs with multiple people and on average to keep the solid drop you have to change the wind between 4 & 6 MPH to match to up. I find no discussion of Windage corrections with any consistency and believe most out there just walk in the wind and rely on drop alone. It's rarely mentioned.

Out here, most matches are 1 shot only, (Avg Tgt is 1.5 MOA) under field conditions with a lot of uncommon ranges and winds averaging 10 to 15 MPH. I have shot these local events, my training videos, and taught classes under these conditions (weekly) while running multiple software solutions at the same time. I have also been to no less than 4 Gunsite XLR Classes using multiple solvers and found the same issues. In all I do my best to record real, practical data with multiple calibers from 6mm to 338.

Given the the choice, the Pesja solutions are better with both drop and drift. It's so noticeable it cannot be ignored, especially with drift. The drop can be considered a wash. Both Field Firing Solutions and Coldbore manage the published BCs much easier, require less "Truing" (especially with common loads) and in the case of FFS will only work with G1 numbers. It's like .496 it was the law of the land for far too long which leads me to wonder what the "Apps" are doing to have to lower it. For background, I graduated the USMC Sniper School in 1986, and have taught and continued to advance in the field to this day. That is a lot of history and experience to draw from. It's not like yesterday I missed and today I can finally hit something.

I don't want to talk out of school but it was presented to me that several current .mil shooters are experiencing the same issues but refuse to speak up because of the politics involved. Rocking the boat is frowned on, me on the other hand have the reputation of doing just that. I ran both Coldbore and JBM at the Grind, with a 260REM using a 136 Scenar L @ 2800fps I barely held off the plate out to 800 yards, the most windaged used was .3 to .5 mils. Just a few shots at best. So it's easy to mask the potential problems. Last time at K&M using a 6mm Creedmoor with Berger 105s @ 3150 I never held off the plate out to 1000. So you wouldn't notice it. ( for the record I love using Berger bullets and using the older AB loaded 175s I have beat many 6.5s and 6s here locally)

I am not sure it's the BC as much as the software. I think trying to follow the original model is flawed which is why I find Pesja solvers to work better. Why default back 100 years when someone came up with a better model much more recently would be my question? Guys say it's flawed but still when the G question comes up they talk ancient history. If you're gonna modify it, do so on a manner that isn't quoting something older, we have reliable data for G1 just fix the model to match instead of handicapping it. Or do every shooter a favor and band them all, seems a better way to do it ( I say that grinning). I mean if JBM can default to a banded G1 solution that is spot on, I don't see why we aren't doing that. After all, we have a much bigger variety in barrels, bullets, powders and especially shooters, an average is no longer valid. One size clearly does not fit all. By the way, was that barrel, 1-10, 1-11.25, or maybe it was number 87 in the run and was actually 1-10.69 ? I know Bartlien can carry the decimal to 4 places... My 6CM is a 8-7.7 gain twist, I have a 338 for monolithic bullets that is 13-5.4 lol put that in your software.

 

[damoncali]

I think it's strange that you're picking on Berger, who of all the makers has gone to pretty great lengths to give us accurate numbers, and the only bullet maker to make detailed data available (via Bryan's book) on what those measurements are comprised of. Heck, Sierra still publishes velocity dependent G1's and no G7's at all! Don't get me started on some of the nonsense that comes out of the small custom makers. Some of Litz's published data is a little sparse. But some data is better than no data. And he also provides uncertainty estimates, which is a great thing. I'm not aware of anyone else who does that.

Is any company going to be perfect? No. Is anyone going to care about some detailed explanation about how the measure/calculate their BC's? Not really. I think it's cool. But most people just don't care and they have a business to run. It's not a science project. Practically speaking, if you plug in Berger's numbers and accurate inputs into any off the shelf point mass calculator, you will be pretty damn close out to 1000 yards. I can't see why Berger or anyone else would invest the thousands of dollars it takes to hone the last tiny bit of precision out of BC measurements that only a handful of people care about, especially given the substantial lot to lot variations.

One area where I think Berger may deserve a little pushing is in their reloading manual, which implies that it's basically compiled from QuickLoad rather than physically tested. They don't say clearly one way or another, but I would like to know if I'm using software- generated data or physically tested data.

 

[Michael Courtney]

BC and Wind Drift issues

Much of this discussion came up at the GAP Grind this past weekend. Including several .mil shooters, so it's actually quite timely.

In my personal experience, even today I find .496 to work better. ( though i like and use Sierras banded numbers most of the time, as listed above ) I think the "modified" part when talking about Point Mass is being purposely unkind to any original G1 value. And regardless of the G value used (G7 or G1) it was the general consensus that while the drops are very good in most of the current Point Mass solvers used, (everyone you talk to praises the drop) the windage is no where close to correct. I know I have been running multiple programs with multiple people and on average to keep the solid drop you have to change the wind between 4 & 6 MPH to match to up. I find no discussion of Windage corrections with any consistency and believe most out there just walk in the wind and rely on drop alone. It's rarely mentioned.

Lowlight, thanks for some astute observations.

BC accuracy of specific bullets is an essential prerequisite for addressing more fundamental questions in ballistics. Here, the fundamental question is the accuracy of the approximation made by most modified point mass ballistics solvers that wind drift depends only on the horizontal component of the wind velocity perpendicular to the line of sight, the bullet's BC, and the muzzle velocity. Specifically, this method assumes no dependence of wind drift on mass (other than how BC depends on mass), on bullet length, on bullet stability, on twist rate, or on how the total drag is distributed along the bullet (nose drag, skin friction, base drag, etc.)

I prefer to frame the question in terms of the accuracy of predicted wind drift, because I usually assume no prediction is perfectly accurate (say to 1 part in a trillion), but the real issue is whether the predictions are accurate to 1%, 5%, or 50%. Lowlight's observations suggest that the predictions may be errant by as much as 50%, which he seems to ascribe to errors in the method itself. Nick's observations seem to suggest an error closer to 10% which he ascribes to an inaccurate BC for Mach numbers between 1.0 and 1.2. I think more careful experiments are needed to address these fundamental questions.

One experimental challenge in testing predictions is the need to know the wind magnitude and direction at every point along the bullet path at the instant the bullet passes. Picture an array of Kestrels, mounted on weather vanes (as shown in the picture), every 50 or 100 yards along the bullet's flight path, with their heights adjusted according to the height of the bullet flight path at each distance. If the Kestrels are communicating wirelessly with a centralized computer and timing issues are attentended too, such a system represents a much more accurate test of wind drift predictions than a single handheld Kestrel at the firing point, even when combined with skillful interpretation of wind flags.

We've designed some experiments like this, and I think Nick has also. There are some more advanced methods of measuring cross winds along the flight path, but they are very expensive. The more realistic approach is a wireless anemometer with sufficiently fast response, mounted to a vane to provide both magnitude and direction information synchronized to the passing of the bullet. One challenge in performing the experiment at 1000 yards is that the bullet is close to 12 feet above the line of sight at its apex, and it is well established that wind speeds tend to be greater up there. For this reason, we designed experiments with bullet BCs (G1) closer to 0.300 and a target range of 600 yards to keep the bullet heights within 4 ft of the line of sight to facilitate keeping the anemometers and weather vanes at the proper height.

But we also designed a much simpler experiment to test the accuracy of the fundamental assumption of most modified point mass solvers. One need not actually measure the wind speed and direction every 50 to 100 yards along the flight path if one simultaneously fires three to five different bullets with the same BC and muzzle velocity. Our experimental design picked a BC of 0.29 and a muzzle velocity of 2800 fps. Keeping the range to 600 yards also reduces other sources of dispersion and eliminates drag variations that come into play at lower Mach numbers.

The approximation used by the modified point mass methods predicts that a 53 grain .224 boat tail bullet, a 62 grain .224 flat base, a 110 grain .308 boat tail, and a 220 grain .308 flat base will all have identical wind drift if they have the same BC, muzzle velocity, and are fired simultaneously over the same flight path. The percent differences in measured wind drifts would serve as a measure of accuracy for the method used by the modified point mass, without needing to carefully measure the wind speed and direction at a number of points along the flight path. Of course, one must confirm the BCs are the same for this experimental design to serve its purpose.

 

[damoncali]

There is a reason they came up with the 6DOF method and did all that work to figure out all those coefficients. It's because a single coefficient is incapable of capturing all of these dependencies. Your BC becomes a variable dependent on many other variables. The next thing you know, you need 30 coefficients to calculate your BC, and you're back where you left off with the 6DOF solution, except none of your coefficients actually mean anything. This is not progress.

The real progress to be found is in the ability to accurately measure the wind in real time along the path of the bullet. If you can do that, none of these details will seem particularly important. Point mass is good enough. Garbage in garbage out.

 

[Michael Courtney]

There is a reason they came up with the 6DOF method and did all that work to figure out all those coefficients. It's because a single coefficient is incapable of capturing all of these dependencies. Your BC becomes a variable dependent on many other variables. The next thing you know, you need 30 coefficients to calculate your BC, and you're back where you left off with the 6DOF solution, except none of your coefficients actually mean anything. This is not progress.

There are only a few ranges in the world that can measure the coefficients needed for the 6 dof solution. I think the goal here is to better approach more accurate 3 dof solutions with instrumentation that is available for a few thousand and not out of reach for advanced hobbyists. Approaching the problem with velocity dependent Cds or BCs gives a very precise physical meaning to however the problem is described in terms of drag coefficients. A small number of additional parameters my be needed to tweak the modified point mass wind drift model if additional adjustments for bullet mass, length, stability, twist, etc are needed. But first we most address how this would work and whether we need improved models or better drag measurements at low mach numbers, or both.

The real progress to be found is in the ability to accurately measure the wind in real time along the path of the bullet. If you can do that, none of these details will seem particularly important. Point mass is good enough. Garbage in garbage out.

Your pride in 6 dof models is worthless when addressing the problem of real time measurement of wind velocity vector fields and computing windage adjustments quickly enough to fire the shot before the wind changes. There simply are not battery powered portable computers available to do the 6 dof calculations in real time; whereas, there are computers fast enough to solve the modified point mass and similar approaches fast enough.

Is modified point mass really good enough if one has the wind velocity vector field and velocity dependent BCs or Cds to 1-2%?

This is where the question gets back to whether the current wind drift model (depending on BC and MV only) is accurate to 1%, 5%, or 50%. If the model itself is off by 10% or more, windage can be off by enough to miss at 1000 yards with the 175 SMK, and in all cases, you'll be missing long before the bullet goes subsonic in moderate cross winds even with the very high BC bullets out of .300 WM, .338 Lapua, 50 BMG, etc.

 

[Christopher Rance]

A economical wind sensor array exists.
WSA | Applied Ballistics, LLC

On other calculators (not AB), the BC is typically scaled. This results in an artificial scaling that not only affects the drop, but also the time of flight. That changes the wind deflection as well. But through extensive tests on instrumented ranges where wind sensors are present, the AB team have seen that only the drop needs to be scaled, not the wind. In fact, you'll tend to over-estimate the wind's influence on a round if you scale the BC like other solvers do.


A great article from Dan, who's been in the business of "wind" for a long time.
http://www.nvisti.com/wp-content/uploads/2014/06/NVDOC1403-Wind.pdf

 

[Lowlight]

In the field, your access to real time accurate data is limited, with as much weight as we put on the elevation, it has clearly been demonstrated that wind is even more so important. After all for the .mil shooter as an example, you have a lot more room with elevation errors on a human target than with wind. We stand taller than we are wider.

So you have a ton of emphasis on what it takes to line up the elevation, but the focus for windage errors revolves more around Spindrift than with the actual wind solution. Sure it's easy to dismiss it and say, "well you can't predict the wind, but we can tell you what the SD is, so be sure to dial that ", however I believe that is a cop out. A way of changing the conversation, after all, it's been proven that not using the SD will still get you a 1st round hit, but not using wind will not. We see far too many people mention SD over the real issue, the wind. And I am not so sure you can skim over it saying it's the lack of complete wind data. We can clearly "group" on target without it being a completely strung out horizontal deflection. Once we're there rarely are you being blow off every other shot.

When I am on the line with a group of students, and see them continuously hit a piece a steel that is 1.5 MOA wide, and in order to line up the wind solution (actual) to match the solver, me having to reduce the wind call in the computer by 4MPH or more is a problem with computer not the reading. You can't tell me that using my Kestrel at the shooter with a reading of 10MPH then needing to reduce the reading to 6MPH in the solver is the fault of the wind call. Especially today when we have a lot more students with 6.5s than .30 cals on the line. My next question is, how come this doesn't happen with ColdBore as an example, but it does with most Point Mass solvers. It because the air is less dense in CO and nobody using Point Mass is accounting for this ? Because I have spoke to Gus Ruiz about this and his solver adjusts the wind for the air density. Is PM saying 10MPH at sea level is the same as at 5000ft above ? That might be it ...

if the question is with the wind call itself why not use multiple wind zones, we can confirm within 1 MPH or better wind at the shooter, that is a given. The next step is to divide the shot into the other two zones. Yes, if you are moving up in a wind gradient by firing at or beyond 1000 yards or more, I would certainly expect at least 2MPH added to the solution for the increase in velocity because we have less drag off the ground. (Wind wise) but less... some are using multiple zones and changing the down range zone to match up the actual wind used should be the next step. After all we need to record our actual drop and drift, either in the datebook or using the computer to "true" the solution to our system. (the system includes you, which no computer can account for)

The reality of it, "averages" are clearly not working and continuing to fight for the best "average" is wasting all our time. We need to work out better solutions for drops in velocity like banding does and make that the rule and not the exception, as well that should also work the same way with the wind. When targets are 20x40, 18x30, or any other taller vs wider, the wind is what matters more to get that hit. I am absorb a 2 MOA error in elevation but I cannot do the same with windage. Sure we have round and things like animals that are wider vs shorter... but still overall, I would rather the focus be on proper wind over being told to add in SD. That's not it, we're driving the bullets faster those numbers are shrinking. With a high velocity bullet I can also absorb a lot more elevation errors as with an Unknown distance target, still the wind is only be cut marginally when compared.

My experience tells me it's a solution error and not a wind reading one. It's too easy to dismiss the wind and blame a lot of other things which I get, but lately all my focus has been on the wind and I am seeing some glaring problems with some things and not with others.

 

[Christopher Rance]

In the Army we do use wind zones with the foundation beginning at the shooter since we have a device that can measure the wind within .1 m/s. From there I have a starting point and with the wind in the first third generally being the wind with the greatest influence 1k and in, I simple add or subtract .2 or more mils based on my observation of wind in the 2nd and third zones.

In the school they teach the Acc 1st wind formula
Range x wind + wind=fv mil hold:
Wind factor derived from BC
.4 308
800 m and in (effectiveness)

Each range has a value ex.
100 m = .1
600m = .7 (bumps up .1 after 500m)
800m = .9

You divide wind read 12mph FV by BC value (.4 for .308) = 3 if you have anything remaining you just add it to that.

So targets at 500 meters, L-R FV wind at 12 mph = 1.5 mil L hold. Pretty simple but it's a minute of man solution.

I like pulling a live capture at my spot, let AB compute a fire solution then adjust as I see fit. Lately, I just throw the Kestrel in a vane mount, let it capture live feed, then just pull the data from my android device and the Kestrel companion app. I can keep that AB kestrel in the mount and adjust it from the tablet. Been working like a charm on Larue poppers out to 800m in some medium winds 6-12mph. If I'm back in the Stan in an OP/defensive posture, I'm gonna run it just like that. Better then starting off with a guess.

When I look DownRange at 800 m, all I know for certain is the wind is blowing. No way a human can estimate within 1mph at that distance without an aid like a sensor or a first shot to act as a spotter round.

 

[Michael Courtney]

A economical wind sensor array exists.
WSA | Applied Ballistics, LLC

On other calculators (not AB), the BC is typically scaled. This results in an artificial scaling that not only affects the drop, but also the time of flight. That changes the wind deflection as well.

I've been comparing results from Bryan's calculators with JBM for a long time. The calculator that came with the book in 2009, the Berger calculator released at about the same time, and the current calculator at the Berger site, all agree with JBM predictions within 1% or less for a number of trials out to 100 yards. Often the agreement includes all the digits of the output. It is hard to believe that one of these calculators is doing anything significantly different from JBM. Please explain if you mean there really is a difference.

The array of wind sensors is impressive, but my concern is the need to get to 12 feet above the line of sight needed midrange for 1000 yards. Our design calls for using much heavier and robust tripods even to get to the 4 ft above line of sight needed midrange for 600 yards. For 1000 yards, we'd pretty much given up on completely portable systems due to the challenges of getting the sensors 12 ft higher than the line of sight in a good wind.

But through extensive tests on instrumented ranges where wind sensors are present, the AB team have seen that only the drop needs to be scaled, not the wind. In fact, you'll tend to over-estimate the wind's influence on a round if you scale the BC like other solvers do.

To be sure this is the real issue, the mid range sensors need to be 12 ft above the line of sight where the bullet path really is (and appropriately adjusted at each range).

A great article from Dan, who's been in the business of "wind" for a long time.
http://www.nvisti.com/wp-content/uploads/2014/06/NVDOC1403-Wind.pdf

[/QUOTE]

This is a nice article and recommended reading. But this article is really focused on the predictions of Bob McCoy's modified point mass model and how it predicts wind drift. There is nothing in this article to suggest what level of accuracy can be expected if one has very accurate velocity dependent BCs and wind speeds and directions along the bullet path.

Your comment about scaling the drop but not the wind seems odd, since (according to McCoy) they both should depend only on the time of flight at a certain point. Why would it make sense to scale an input when computing the time of flight to compute the drop, but not to scale an input computing the time of flight to compute wind drift?

Since drop depends on time of flight and some simple physics formulas, it's hard to imagine drop gets computed with anything other than the physical, most accurate possible time of flight. Maybe something gets scaled earlier to compute the acceleration along the bullet path.

 

[Lowlight]

Chris,

I am well aware of that, I am talking about solvers and not rule of thumb formulas, as well I am also hip to the first round / believe the bullet part to correct.

But the goal should be for the ballistic solver to be every bit as accurate with wind as it is with drop. I see too be a discrepancy when comparing the Point Mass solutions to those of FFS or CB 1

 

[damoncali]

Your pride in 6 dof models is worthless when addressing the problem of real time measurement of wind velocity vector fields and computing windage adjustments quickly enough to fire the shot before the wind changes. There simply are not battery powered portable computers available to do the 6 dof calculations in real time; whereas, there are computers fast enough to solve the modified point mass and similar approaches fast enough.

I'm not suggesting that you need 6dof for every shot. I would say that trying to make BC a function of multiple interdependent variables is a fools errand, and is exactly why the 6dof model exists in the first place. When you make the BC dependent on sg, twist, velocity, and more, all of which interact with each other, you wind up with a very complex situation that rely so a bunch of hard to get data, sort of like the 6dof. Sure, you could maybe come up with a fancy way of building all that supplementary data into a point mass solver and wind up with slightly better results, but it won't be repeatable or even manageable unless you can isolate the effects and model them physically - which again gets us back to 6dof. And if it's not repeatable and generally applicable, you might as well have a table of empirical data.

 

[mil_coder]

Hey guys, I did write to a lot of this in Modern Advancements in Long Range Shooting. In there, I presented a couple of graphs regarding how many anemometers are needed on a 1000 meter path as well as what your expected probability of hit would be. As I mention, things are very terrain specific, but if you take a look at the macro-level summary of the data, that's how it all applies and the probability of hit that you can expect to see.

Regarding the height above the ground... we've done this and put anemometers at the trajectory of a 175 gr SMK out to 1000 meters. Yep, we put them up at close to 30 feet in the air in order to match the trajectory - we used huge wooden towers that were hand built to do this. We ran anemometers at line of sight as well and then compared the drift from each of them.

So, what were the results? There's virtually no difference in the probability of hit on an IPSC target.

While it is well documented that the wind scales as a function of the height above the ground when looking at long term averages, this does not apply for instantaneous measurements. Because the earth's surface is a turbulent boundary layer, at any (short) point in time, the wind at the trajectory of the bullet may be lower than that along the line of sight. You see all kinds of eddies and other things that are dominating the wind conditions. In the bullet's flight time, you can't systematically say that the wind speed is higher above the ground in the turbulent region near the earth's surface.

That being said, it's best to do it with ultrasonic anemometers as well. The typical Kestrel/tripod is a great first order approximation but there is much that can be learned about the wind when using high speed ultrasonics. The mechanical inertia that is in the Kestrel/tripod smooths the data more than you'd like when doing this type of analysis.

When talking about what kind of probability can be expected by using the "average" wind speed over a profile - that is somewhat answered in the same chapters.

If you are reading mirage and good at it, then that's actually a very good average of the entire path. The "mirage" that you are seeing is the light that is arriving from the target and passing through all of the turbulence from the target to your eye. Therefore, it's a very good average. If you can either read that visually or with an optical wind measurement device, then you can achieve probabilities of hit between 50-70% if you just take the average wind speed.

Specific situations can be contrived to show that the average wind speed breaks down, specifically placing high winds at the end of the bullet's path, but for the most part, the average wind works very well.

Also, something of interest to is to look at the probability density function of the wind. It follows a Weibull distribution - not a normal distribution.... that means the mode != mean most of the time and there are better times to shoot than others as well.

Anyway, that's all contingent upon having a good ballistics engine running behind the scenes. One of the things that I have been very careful about when using any ballistics computer is how it computes the wind's influence on a bullet. There have been many calculators in the base that used BC manipulation to match drop, but when you apply it to drift, it drastically overestimates the wind's influence. This is primarily because it's artificially increasing the time of flight information internally and then simply using the lag time to compute bullet deflection.

 

[Lowlight]

So to put it in plain language, are you saying that "truing" has the potential of changing the wind solutions, so while you can true your drop, you risk losing the accuracy of the predicted drift ?

As you said, manipulation of the BC has the unintended consequence of changing the other side of the equation ?

If that is the case, doesn't lend to the reinforce the Pesja solution of using the DK Factor to adjust ? Bending the curve versus changing the factors (BC & MV) of both drop and drift ? Could this explain why "real world numbers" appear to work better vs having to "tweak" the recorded values in the other solvers ? Not being a G dependent solution seems to favor "averages" much better, especially in practical use with the limitations we have in the field. The argument has always been the modifications to what is "really" happening using the old definitions but here it would seem to be a smarter way to address the changes we see.

 

[damoncali]

The point mass method, correctly implemented, does not differentiate between windage and drop - it just calculates x, y, and z of each step of the trajectory. There isn't a separate wind calculation. Changing the BC will necessarily change both drop and windage. In theory, if you improve one, you should improve the other - assuming that the other inputs are all correct and the drag function is appropriate.

 

[Lowlight]

Clearly not... but then again it's not uncommon to ignore the facts on the ground.

 

[damoncali]

That's why I said "in theory". Just explaining the way the model *has to* work. You can't separate wind and elevation with point mass unless you manually add some kind of factor in, in which case, it's no longer the point mass method - it's something else.

 

[Michael Courtney]

I'm not suggesting that you need 6dof for every shot. I would say that trying to make BC a function of multiple interdependent variables is a fools errand, and is exactly why the 6dof model exists in the first place. When you make the BC dependent on sg, twist, velocity, and more, all of which interact with each other, you wind up with a very complex situation that rely so a bunch of hard to get data, sort of like the 6dof.

Agreed. But BC should be determined by the slowing of forward motion alone, without regard for wind drift. For any bullet, BC should depend only on velocity as determined by experiments measuring the slowing of forward motion.

The question then becomes, can wind drift predictions be improved by adding considerations other than BC?

First we must answer how accurate are the wind drift predictions using only BC and MV? If they are within 1-2%, the theory is good enough and we need only focus on acquiring the necessary real time wind data. But if the wind drift predictions based on BC and MV can be off by 10% or more (a lot more) as some are suggesting above, then we need to figure out how to fix the theory to improve the predictions. Will we need a bunch of hard to get parameters like 6 dof? I don't know, but I think I'd first work to correlate deviations from the modified point mass predictions with easily obtainable parameters like mass, sectional density, muzzle spin rate, bullet length, simple stability estimates, ratio of nose drag to base drag, etc. If the deviations from modified point mass predictions correlate strongly with parameters that are already input into the solvers (or parameters that are easily computed from existing inputs), then reducing the inaccuracies in the current models will be straightforward.

Sure, you could maybe come up with a fancy way of building all that supplementary data into a point mass solver and wind up with slightly better results, but it won't be repeatable or even manageable unless you can isolate the effects and model them physically - which again gets us back to 6dof. And if it's not repeatable and generally applicable, you might as well have a table of empirical data.

I don't think it necessarily needs to be fancy or include much supplementary bullet data that the solvers don't already have or can't be input easily (like bullet dimensions). If the method is already at an 80-90% accuracy level (10-20% errors), trimming those remaining errors would be straightforward.

 

[Deleted member 10043]

Wow, this goes back to 2010, OP? Your question is a double edged sword. Most published BCs are predicted and then trued so they are measured. I guess you are more interested if they were measured in real time going down range. That is a tall order for even for Berger to fill and keep everybody happy.

As an aside, I find the four level G1 BC more realistic than G7 for elevation and I don't really know the difference between Point Mass and Pesja. I'm just relaying what I have been experiencing with computer apps. I can rely on the drop with room to spare but the wind calcs are not right. I know that now but then there is the actual wind factor that is going on like two or more different directions and speeds along the way to the target area. Sometimes I find there is no correction other even though the wind is pulling my leg. I'm afraid no computer app is going to help us on the windage every time. Reading the wind is a talent that can be learned but some people are better than most. I'm one of most people.

What would be interesting to measure is going back and converting to group size all the Wimbledon Cup champions' scores and see just how much more accurate things have become over the decades. Personally, I'm just trying to shoot a group the size Ben Comfort shot in 1935. I'll never make it.

 

[Michael Courtney]

The point mass method, correctly implemented, does not differentiate between windage and drop - it just calculates x, y, and z of each step of the trajectory. There isn't a separate wind calculation. Changing the BC will necessarily change both drop and windage. In theory, if you improve one, you should improve the other - assuming that the other inputs are all correct and the drag function is appropriate.

Taking a simplified case of a horizontal line of sight, define this as the x axis, the perpendicular horizontal, define as y, and "up" defined as z. The only force in the x direction is air drag, which is given by the drag force equation. The only force in the z direction is gravity. The only force in the y direction is the wind force.

Write down the kinematic equations, integrate numerically with Runge-Kutta, and you have your predicted trajectory.

The big flaw is in how the wind force is computed as depending only on the cross wind component and the BC which is defined to relate to the retarding force in a perpendicular direction. Why should the wind drift depend only on the forward retarding force and be independent of mass (except for how mass is included in BC) and be completely independent of bullet length and cross sectional area the wind sees from the side?

Would it make sense to compute a cross current's effect on a boat only from it's drag in the forward direction, completely ignoring its drag profile from the side? This is how wind drift of bullets is computed by relying on BC and MV only.

 

[Michael Courtney]

Hey guys, I did write to a lot of this in Modern Advancements in Long Range Shooting. In there, I presented a couple of graphs regarding how many anemometers are needed on a 1000 meter path as well as what your expected probability of hit would be. As I mention, things are very terrain specific, but if you take a look at the macro-level summary of the data, that's how it all applies and the probability of hit that you can expect to see.

I gotta get that book. Thanks for the preview.

Regarding the height above the ground... we've done this and put anemometers at the trajectory of a 175 gr SMK out to 1000 meters. Yep, we put them up at close to 30 feet in the air in order to match the trajectory - we used huge wooden towers that were hand built to do this. We ran anemometers at line of sight as well and then compared the drift from each of them.

So, what were the results? There's virtually no difference in the probability of hit on an IPSC target.

Fascinating. Thanks for sharing this result. It's nice to see that the SBIR $ was put to good use.

While it is well documented that the wind scales as a function of the height above the ground when looking at long term averages, this does not apply for instantaneous measurements. Because the earth's surface is a turbulent boundary layer, at any (short) point in time, the wind at the trajectory of the bullet may be lower than that along the line of sight. You see all kinds of eddies and other things that are dominating the wind conditions. In the bullet's flight time, you can't systematically say that the wind speed is higher above the ground in the turbulent region near the earth's surface.

Once again, fascinating. I'll probably read this paragraph 20 times trying to formulate experiments and consider how to otherwise evaluate it.

For example, consider an experiment with identical low BC .223 Rem bullets fired simultaneously at the same velocity over a shorter course (say 500m) without the huge mid range height, but one 30 feet high and one at normal bench rest level. (Build two towers 30 feet high, one for the shooter, and one for the target.) If your explanation is correct, the wind drift on the upper trajectory won't be systematically larger than the lower one.

And if this is true up to the height of a 1000 yard trajectory, how much higher can one go and still have predictions as accurate from line of sight wind measurements as from measurements along the actual path?

That being said, it's best to do it with ultrasonic anemometers as well. The typical Kestrel/tripod is a great first order approximation but there is much that can be learned about the wind when using high speed ultrasonics. The mechanical inertia that is in the Kestrel/tripod smooths the data more than you'd like when doing this type of analysis.

I like to think about it like a low pass filter, more or less giving a "moving average" over a short time interval rather than a true instantaneous reading. The time window for the vane is longer than for the anemometer.

But I am perplexed as to why the moving average over a short time window would matter more than the difference in wind 30 feet higher or the effects of spatial averaging over large fractions of the range to the target. Certainly, the ultrasonics give more insight into the time scales on which wind speed and direction are changing, but if you ran the ultrasonic results through a low pass filter or moving average mimicking the time scales of the Kestrel vane and anemometer response, would the accuracy of your wind drift predictions suffer significantly?

Anyway, that's all contingent upon having a good ballistics engine running behind the scenes. One of the things that I have been very careful about when using any ballistics computer is how it computes the wind's influence on a bullet. There have been many calculators in the base that used BC manipulation to match drop, but when you apply it to drift, it drastically overestimates the wind's influence. This is primarily because it's artificially increasing the time of flight information internally and then simply using the lag time to compute bullet deflection.

Now your tempting me to reverse engineer a number of solvers. With your physics and math background, you will probably get the gist:

Enter the appropriate outputs into a spreadsheet as x, y, z, t, Vx at 1 yard intervals.

Use the basic principles of Calculus and kinematics to compute the Fx, Fy, and Fz at each point. Fx and Fz are simple, they are just the retarding drag force and gravity. But reverse engineering Fy can tell me how these things are really relating BC and cross wind to the force of the wind on the bullet. Something is not right. Of course, it's also simple enough to tell if their drift predictions agree with Eqn 5.2 of Litz 2009 (time lag times wind speed, really going back to Bob McCoy).

 

[Michael Courtney]

So you have a ton of emphasis on what it takes to line up the elevation, but the focus for windage errors revolves more around Spindrift than with the actual wind solution. Sure it's easy to dismiss it and say, "well you can't predict the wind, but we can tell you what the SD is, so be sure to dial that ", however I believe that is a cop out. A way of changing the conversation, after all, it's been proven that not using the SD will still get you a 1st round hit, but not using wind will not. We see far too many people mention SD over the real issue, the wind. And I am not so sure you can skim over it saying it's the lack of complete wind data. We can clearly "group" on target without it being a completely strung out horizontal deflection. Once we're there rarely are you being blow off every other shot.

Lots of insight here. Thanks for sharing these observations. The wind is the real issue. But if we fix the BCs to match the wind drift, we run the risk of messing up the drops and also other things like retained energy and impact velocity and when the max supersonic range. We need another approach.

When I am on the line with a group of students, and see them continuously hit a piece a steel that is 1.5 MOA wide, and in order to line up the wind solution (actual) to match the solver, me having to reduce the wind call in the computer by 4MPH or more is a problem with computer not the reading. You can't tell me that using my Kestrel at the shooter with a reading of 10MPH then needing to reduce the reading to 6MPH in the solver is the fault of the wind call. Especially today when we have a lot more students with 6.5s than .30 cals on the line.

You are right of course, unless you've forgotten to multiply the Kestrel reading by the cosine of the angle the wind is making with 9 O'Clock (or make an equivalent adjustment for wind direction).

But I think it's time to name names on these faulty solvers. Apparently they are not all implementing the modified point mass wind drift method properly. Which one were you using and needing to adjust the wind call down on?

Is PM saying 10MPH at sea level is the same as at 5000ft above ? That might be it ...

I think this is a big part of it. The only way modified point mass accounts for wind drift is in the time lag. But I have a hard time believing that a 10 mph wind at 30% lower air density will move a bullet as much in a given time lag as a 10 mph wind at sea level. True, the lower air density reduces the time lag. But I can't believe the only difference between a 10 mph wind at sea level and 5000 ft is through the extra time to arrive at sea level. Air that is 30% less dense will exert a smaller force sideways on a bullet in a 10 mph wind. It cannot only be a smaller retarding force.

We shot a lot in Colorado before relocating to Louisiana. Wind moves bullets much more in Louisiana. And the difference is more than predicted with the time lag model.

The reality of it, "averages" are clearly not working and continuing to fight for the best "average" is wasting all our time. We need to work out better solutions for drops in velocity like banding does and make that the rule and not the exception, as well that should also work the same way with the wind. When targets are 20x40, 18x30, or any other taller vs wider, the wind is what matters more to get that hit.

That's why I love the steel prairie dogs to separate the men from the boys in the precision rifle contests. Maybe F-Class needs tall, thin ovals rather than circles.

My experience tells me it's a solution error and not a wind reading one. It's too easy to dismiss the wind and blame a lot of other things which I get, but lately all my focus has been on the wind and I am seeing some glaring problems with some things and not with others.

I tend to agree, but it's hard to pin the blame on all modified point mass solvers now that the claim has been made that some are implemented incorrectly. Can you email me the output of your solver to compare with others and see if the implementation yours is using makes one of these scaling errors spoken about above? [email protected]

 

[damoncali]

Would it make sense to compute a cross current's effect on a boat only from it's drag in the forward direction, completely ignoring its drag profile from the side? This is how wind drift of bullets is computed by relying on BC and MV only.

If you believe that the bullet generally aligns to the air flow and that any minor yaw is accounted for by BC, then yes. In fact, if you want to argue that wind should be dependent on some sort of sideways BC, you must also argue that drop is subject to the same phenomenon and we're back where we started. The bullet doesn't know the difference between wind and falling.

In other words, how is the bullet, which is round and spinning, to know one direction from another?

 

[Michael Courtney]

If you believe that the bullet generally aligns to the flight path and that any minor yaw is accounted for by BC, then yes. In fact, if you want to argue that wind should be dependent on some sort of sideways BC, you must also argue that drop is subject to the same phenomenon and we're back where we started. The bullet doesn't know the difference between wind and falling.

In other words, how is the bullet, which is round and spinning, to know one direction from another?

The ultimate test of theory is not argument from causation, but rather experimental data. Where is the data confirming the accuracy of your theory to 1%?

A bullet knows which direction is down, because gravity is pulling on it in that direction. The force of air drag pushing a falling bullet "up" would not equal to a 10 mph cross wind until very late in the trajectory when it was falling at 10 mph. It's effect on the vertical motion would be no bigger than turning on a 10 mph cross wind very late in a trajectory, and it might be even harder to detect if it masked by other effects: lift (from an upward component of the yaw of repose), vertical Coriolis, local and altitude variations in the acceleration of gravity compared with what the solver is using.

Have you ever tried to measure the drag coefficient on a falling lead object over a short distance? It's almost impossible. You're going to see the local variation in g before you get any reasonable estimate at all of the drag coefficient. It can be done with a 1 million frame per second camera with a known grid in the background. Once you have the local g to 0.01% from motion early in the fall, the drag should show up as deviations from 0.5 g t^2 late in the fall. It's easier to do some trials zoomed in at the top of the fall to get the local g, and then zoom in at the bottom of the fall and get the drag from deviations from v = sqrt(2gh) because the slowing is easier to detect than the change in drop distance. Once you have the velocity at the bottom of the fall, you run some guess and check drops and adjust the Cd until your velocity at the bottom matches your experiment. It is much easier to launch an object horizontally at a known velocity and infer Cd from the observed velocity loss over a measured distance. This is because the drag force is acting strongly across the whole path and not just turning on strongly near the end.

I am not doubting that the strongest contributor to wind drift is well approximated by the time lag times the cross wind speed. I am questioning the accuracy of this approximation (because it assumes the bullet axis aligns instantaneously with the flow field), and the assumption that the lateral component of aerodynamic drag given by the forward Cd and bullet speed is the only lateral force acting on the bullet.

Whether or not horizontal drag needs to be accounted for explicitly should be an experimental rather than a theoretical question. I would hypothesize that accounting for the air density is likely to be more important. Wouldn't you expect the alignment of the bullet with the flow field to be slower in thinner atmospheres? There are two ways to think about this: 1) If the air drag resisting forward motion is reduced by 30% due to a 30% reduction in air density, the bullet should align to changes in the air flow more slowly. 2) Reducing the air density by 30% increases the gyroscopic stability by about the same factor which makes the spin axis more rigid and resistant to the point of the bullet changing direction.

This may be an issue of confirmation bias (which is why real, carefully controlled experiments are needed), but many shooters have reported to me their experience that heavy bullets tend to resist wind drift better than lighter bullets to a larger degree than expected from their BC. Have you any experimental data showing otherwise, say that a 220 grain bullet with a BC of 0.3 will move as much in the wind as a 53 grain bullet with the same BC and muzzle velocity?

 

[mil_coder]

So to put it in plain language, are you saying that "truing" has the potential of changing the wind solutions, so while you can true your drop, you risk losing the accuracy of the predicted drift ?

As you said, manipulation of the BC has the unintended consequence of changing the other side of the equation ?

If that is the case, doesn't lend to the reinforce the Pesja solution of using the DK Factor to adjust ? Bending the curve versus changing the factors (BC & MV) of both drop and drift ? Could this explain why "real world numbers" appear to work better vs having to "tweak" the recorded values in the other solvers ? Not being a G dependent solution seems to favor "averages" much better, especially in practical use with the limitations we have in the field. The argument has always been the modifications to what is "really" happening using the old definitions but here it would seem to be a smarter way to address the changes we see.

Frank - Indeed that is what I am saying. Is that "truing" has the potential of changing wind solutions, so while you can true the drop, depending on how things are implemented within the ballistics engine, you definitely risk losing the accuracy of the predicted wind drift. Most people don't realize that at all though because they don't have access to a range instrumented with a ton of anemometers.

Because we have accurately collected drop, muzzle velocity, and data for wind information as well as the atmospherics, bullet, gun, and all other parameters, we can perform a lot of experiments with this data. And that's what we've done. We've picked apart a ton of different ballistics solvers and analyzed how they work. We had to for our wind measurement work to make sure that when we decided to go forward with a ballistics solver, that it worked correctly for drop and wind drift.

I've said it before but it's particularly relevant here, that any properly written solver, regardless of the method it is using, should produce the same results. I've looked at solvers that ran Pejsa methods, Siacci methods, and also modified point mass models. If you have the same analytical model, look up tables, or drag curves, respectively modeled in the solver, then the solutions will match very closely.

Given such a baseline set of conditions, it's difficult to see much difference between them. Where things start to greatly differ between them is in how each of them handles "truing" and also what inputs each of the solvers can accept.

I won't mention specific solvers names here and so I will just call them solver X and solver Y for the moment. Solver X had an interesting method of performing truing. You could perform muzzle velocity truing in the supersonic region - which is all good - especially if you don't have a chrono. But then it did something very odd. It appeared to use banded BC's. It allowed for you to enter in BC as a function of range. At first, I assumed that meant that that it was using banded BC's. But upon closer inspection, what it was doing was using the BC that you entered at the given range and applying it to the entire flight path.

In other words, let's say that you trued the BC at 800 meter and you entered a value of 0.50 to get the drop to match up (made up numbers here for simplicity). At 1000 meters, let's say you would find that the BC would be 0.450. In the case of shooting to 1000 meters, when you shot, it was literally applying the BC of 0.450 to the ENTIRE path. Ouch! What that means is that if you input the measured wind values into the solver, that it would drastically over-estimate the wind drift. Because the BC was lowered to get drop to match up, then time of flight was affected, and thus the wind deflection was computed incorrectly. This would largely go unnoticed unless you have a wind sensor array like we do or an optical wind measurement system. Nonetheless, we eliminated solver X from consideration.

Next, we took at look at solver Y. Solver Y did something equally strange. It required us to enter in data at multiple points in the path using drop data. We'd have to enter in all of the environmental parameters manually at each point along the path and then it appeared to clamp the measured drop value to a fixed value at that range and set of atmospheric conditions. Therefore, if we ever saw that condition again, then it would know to look that up in the table. It didn't appear to be modifying the drag curve at all and instead building some kind of a look up table (a drop table, essentially). The down side to that method is that since it only clamped the data at a single range, we would have to shoot at multiple ranges. The other odd thing is that it didn't seem to care what you entered for the muzzle velocity either. I could put nearly anything in as the muzzle velocity and then build up this drop table and it used that. Now, that's an interesting method for getting the drop correct, but as you can already see, this really messes up when you put the real wind data in. If your original muzzle velocity was not absolutely correct, then your wind deflection is off. If your MV is too high, then your wind deflection is is too little. If your MV is too low, then the computed wind drift was too high. Grrr... Oh... and once I had drop data entered, it didn't let me enter in muzzle velocity... Weird.

I haven't tested FFS, so I'd have to see what that one does with "truing" data. But it's something that I am willing to do.

Now, I know this is getting to be a lengthy post, but I do have a point in mind here... There's a right way to get both the wind drift to match up as well as the drop as well. It goes back to pretty much what damoncali said here. A modified point mass model with an accurate drag model for the bullet of interest is the most universal and best way to do this.

Using a drag curve for that specific bullet, plug that into a properly written MPM solver. Make sure you account for some of the other effects like spin drift, Coriolis, and aerodynamic jump. Then, given that you're using an accurate bullet model (a good Mach/Cd table), the largest unknown variable that you have is the muzzle velocity. If you don't have a chrono, you can still get accurate muzzle velocity data based upon drop at a single range that is near the range where the bullet hits Mach 1.2. Adjust it to match up to your drop (please don't do this with just 1 shot!). In this case when using the custom drag curve for that bullet and accurate environmental and muzzle velocity data, both drop and drift match up very well. And if it is a good custom drag curve, then drop and drift continue to match up at long ranges a well. In other words, if you have a good set of inputs and an accurate model of the bullet, you don't have to play this game of trying to get things to match up artificially through modification of BC or a look up table for drop dat at given conditions like solvers X and Y.

One thing that I didn't mention in my earlier post about how we tested the 175 gr SMK is that not only did we look at G1 and G7 data, we also used one of Bryan's custom drag curves as well. Not unsurprisingly, drop and drift matched up at the ranges tested. There was no truing required since we had a good muzzle velocity.

None of this is at all surprising. After all, if you start with a good model of the bullet that you're using, then an MPM solver accurately models the bullet's flight. If you have good wind data like that from an array of anemometers or an optical wind sensor, it's entirely possible to get drop and drift to match up just fine.

Frank - as you point out, facts on the ground are different sometimes. Where people usually have issues is that they don't understand how the wind behaves and usually overestimate the wind. The natural tendency is to feel the gusts and ignore the huge lulls in between those gusts. They also assume that if it's gusting locally, that it means that it's gusting down range... wrong. The best thing to do is do your best to look at the entire path average wind and then use that. Local measurements are good. Statistically speaking, all of our data shows about 30% probability of hit out to 1000 with a 308. However, when you start accounting for the wind down range as well, you see a huge spike in probability of hit just from taking a second measurement. So, you definitely can't ignore the facts on the ground. The problem I see most often is that most guys just flat out can't read the wind. You throw an optical wind sensor out there or a set of anemometers and every single guy is surprised by what they *think* the wind is compared to what it really is...

So, you going to come shoot with me now? Ha ha!