BC Data....truth or dare

[viva la figa]

How reliable is the BC data printed on the Berger Bullets box? Is there a bit of "marketing" built into that number?

The reason I ask is I did a prone competition a few weeks ago and I trued up my muzzle velocity using my dope at 600 yards in Ballistics ARC. Once I did that none of my dope worked. I tried going back to dope I knew worked at another shooting range and a known set of weather variations. I used the same weather inputs my squad mates were using on their kestrel. I could make hits at close range (<600yrds) but not at distance with one set of dope. Then once I got a hit at 900yrds after several misses I used that dope to true my muzzle velocity in the app. The result being that my shots at close range were off.

Given that the rifle data was then same and the weather was entered accurately why would my MV change from 2890 fps (checked with magnetospeed) and yet when the dope was trued up at 900 it said my MV was 3190

 

[Matches Malone]

Dare

 

[SCKY Shooter]

Bc can b manipulated on your app but weather conditions do actually change minute to minute. You ammo temp could also b an issue. Lots and lots of variables but bad data is a problem. Go to range and recreate the problem. Instead of changing mv change your bc number see what it does.

 

[Long Range 338]

Truing your calculator is not simply a function of MV but also of BC (and all your other inputs have to be correct). You need to true your data at more than one distance and the further the better. 800 is considered the short side of this Even then you need to make sure that the data lines up at shorter distances in between. Best practice is to actually go shoot at several distances and document the drop data and then make your calculator match actual dope.

 

[Matches Malone]

As said above. Also it’s crucial to have some consistency in technique and a good range when truing. One issue I had a long time ago was using an actual ranges known distance. Turns out they guesstimated the target distances past 600y and I trued off some of the further targets past 1000. My dope worked great on that range, not so much other places. Now laser rangefinders are on point so that shouldn’t be an excuse.

 

[SCKY Shooter]

As said above. Also it’s crucial to have some consistency in technique and a good range when truing. One issue I had a long time ago was using an actual ranges known distance. Turns out they guesstimated the target distances past 600y and I trued off some of the further targets past 1000. My dope worked great on that range, not so much other places. Now laser rangefinders are on point so that shouldn’t be an excuse.

Incredible how much distance can make a difference. Actual target distance 1080yrds but posted distance is 1100yrds. That’s .4 difference with factory 6.5creed.

 

[FUNCTIONAL]

Once I chrono my rifle I dont adjust its velocity to match dope. I make sure my environmental inputs are correct from my kestrel (little 2500) and then I just adjust the BC to match my dope.

I dont believe in changing things that are measured to your particular rifle and environment to make something a box says fit your dope. Every manufacturer of bullet I've shot has had a select bullet that is not to advertised...likewise some of the bullets are as advertised. Its not usually a matter of all of Sierra being correct or Berger being more correct. I.E. a Hornady 178 ELDM may be spot on while a Hornady 178 BTHP may need adjusting (for better or worse).

 

[ShtrRdy]

A couple other things come to mind. Did you check your zero after the match? Also, did you try checking your zero when shooting from the same position as you were in when you were having problems?

 

[viva la figa]

Have not been back to the range yet...so limited on the answers I can find there. I was trying to work out what degree of "marketing" was built into the BC number published on a box of 210g Berger hunting vld bullets. Has anyone tested them to see what they are in reality?

 

[ShtrRdy]

Have not been back to the range yet...so limited on the answers I can find there. I was trying to work out what degree of "marketing" was built into the BC number published on a box of 210g Berger hunting vld bullets. Has anyone tested them to see what they are in reality?

Well, supposedly, Brian Litz has been using a measurement technique which gives a reasonably accurate BC on all the Berger bullets. This is much better than some bullet manufacturers who do a calculation on what the BC might be.

Basically, you should be able to use the Berger published BC and only tweak it after you've tried other things.

 

[Dthomas3523]

Use the box BC to get “close.”

True muzzle velocity at <600 yds.

Tweak/true BC >800.

Note the DA and make sure the rest of data is correct.
Anything else is just asking for trouble or people on here to speculate what’s going on.

 

[Dthomas3523]

To many variables such as your individual barrel and fundamentals to figure out how “close” the factory BC is.

 

[TheGerman]

BC on the box is about as accurate as how close to the speed limit people actually drive.

 

[wigwamitus]

I just got some 155.5 grain .308s ... box says .242 (g7) ... Bryan Litz app (AB) says .239 ...if I press "purchase CDM" it usually says the BC is 1.0

 

[Doom]

Use the box BC to get “close.”

True muzzle velocity at <600 yds.

Tweak/true BC >800.

Note the DA and make sure the rest of data is correct.
Anything else is just asking for trouble or people on here to speculate what’s going on.

I could go into an explanation of why this is good advice but the bottom line is this method will account for most of the factors that cause problems at long range.

 

[Steel+Killer]

Once I chrono my rifle I dont adjust its velocity to match dope. I make sure my environmental inputs are correct from my kestrel (little 2500) and then I just adjust the BC to match my dope.

I dont believe in changing things that are measured to your particular rifle and environment to make something a box says fit your dope. Every manufacturer of bullet I've shot has had a select bullet that is not to advertised...likewise some of the bullets are as advertised. Its not usually a matter of all of Sierra being correct or Berger being more correct. I.E. a Hornady 178 ELDM may be spot on while a Hornady 178 BTHP may need adjusting (for better or worse).

I am also in the camp of not changing a data point known to be true (MV CHECKED with a Magnetto Speed) to fit. I will play with the BC until it gets close as can be.

 

[Dthomas3523]

I am also in the camp of not changing a data point known to be true (MV CHECKED with a Magnetto Speed) to fit. I will play with the BC until it gets close as can be.

Used to be in this camp until I realized that “known” is only known to within the accuracy of the device. So it’s reallh not an absolute “known.”

You’ll rarely have to adjust more than 30fps. Considering all the factors, that’s well within margin of error of what the actual velocity is.

Now I trust the math over the device as long as it’s a reasonable difference.

 

[Dthomas3523]

I am also in the camp of not changing a data point known to be true (MV CHECKED with a Magnetto Speed) to fit. I will play with the BC until it gets close as can be.

As an example, magnetospeed advertises a 99.5-99.9% accuracy.

If your chrono’d at 3000, .5% would be +/- 15fps.

Compound that with human error and other things, and that “known” doesn’t sound so exact anymore.

 

[viva la figa]

Pardon my ignorance.....what is DA? Density Altitude?

 

[viva la figa]

My local range has a max 600yrd....so I'll check dope on that. Once I get to where the competition is.....and I can go out past 600yrds....how much should i adjust the BC number by? .001, .01, or .1? How much for starters?

 

[lash]

Pardon my ignorance.....what is DA? Density Altitude?

Yes.

 

[Steel+Killer]

As an example, magnetospeed advertises a 99.5-99.9% accuracy.

If your chrono’d at 3000, .5% would be +/- 15fps.

Compound that with human error and other things, and that “known” doesn’t sound so exact anymore.

I get what you are saying, but a 15fps difference in MV won't even change most firing solutions until around 700yds and at 1000yds only by .10 mil and at 1500yds only by .30 mils. I get nothing is exact but if you can get a known average MV even if it's off by 15FPS I will plug that in and adjust BC and of course try to be as accurate as I can with the other data. This method seems to work for me. Happy Shooting!

 

[Dthomas3523]

I get what you are saying, but a 15fps difference in MV won't even change most firing solutions until around 700yds and at 1000yds only by .10 mil and at 1500yds only by .30 mils. I get nothing is exact but if you can get a known average MV even if it's off by 15FPS I will plug that in and adjust BC and of course try to be as accurate as I can with the other data. This method seems to work for me. Happy Shooting!

+/- 15 = 30.

At 600, that can be .1 mil. That’ll throw you off on a kyl rack.

 

[Diver160651]

My local range has a max 600yrd....so I'll check dope on that. Once I get to where the competition is.....and I can go out past 600yrds....how much should i adjust the BC number by? .001, .01, or .1? How much for starters?

Dthomas3523 is absolutely correct.

Lets take a 115DTAC .620G1 at 3050 (magneto speed) 28inHg, 70°, 50% RH 500y 1" low; 1250y 6"low

500 yards Call U2 1250Y Call 9.3​

1" low at 500 but obviously it looks "centered on steel" You'd not even notice notice unless on paper.​

1250y Actual DOPE 9.4 FIW my actual solution ends up being 3025 .624BC​

Lets do it wrong and see what this does:
Tuning only the BC
I need to CRUSH the fairly universally accepted BC of .620 to .559 to make 500 line-up, that's just unrealistic.
But with 500 dead on using the .559bc - the 1250 prediction U10mils NOW WHAT?????? Your actual shooing 9.4mils

100% trust in the chronograph and only tweaking the BC is the easy way out, but not the correct way..

 

[Long Range 338]

Well, supposedly, Brian Litz has been using a measurement technique which gives a reasonably accurate BC on all the Berger bullets. This is much better than some bullet manufacturers who do a calculation on what the BC might be.

Basically, you should be able to use the Berger published BC and only tweak it after you've tried other things.

Litz is doing this so he can sell the CDM for each bullet. His BC numbers won’t be any better than anyone else’s for your rifle

 

[THEIS]

Hi,

The great exterior ballistic debate of "Tru Dis, Tru Dat".

BCs are NOTHING more than a starting point. There is not a projectile manufacturer advertised BC out there that is going to match the BC you end up with in your rifle, in your shooting area with your shooting position. They ALL need fine tuning.

MVs..well as mentioned already..they are only as good as the equipment thresholds...but lets go one step further in that. The thresholds are then only as good as your shooting consistency. Browse the threads on MVs changing from shooting position changing

IMO Bottom line in firing solution calculations-----Trust Nothing, Verify Everything.

Sincerely,
Theis

 

[Jimgal62]

Hi,

The great exterior ballistic debate of "Tru Dis, Tru Dat".

BCs are NOTHING more than a starting point. There is not a projectile manufacturer advertised BC out there that is going to match the BC you end up with in your rifle, in your shooting area with your shooting position. They ALL need fine tuning.

MVs..well as mentioned already..they are only as good as the equipment thresholds...but lets go one step further in that. The thresholds are then only as good as your shooting consistency. Browse the threads on MVs changing from shooting position changing

IMO Bottom line in firing solution calculations-----Trust Nothing, Verify Everything.

Sincerely,
Theis

Hi,

The great exterior ballistic debate of "Tru Dis, Tru Dat".

BCs are NOTHING more than a starting point. There is not a projectile manufacturer advertised BC out there that is going to match the BC you end up with in your rifle, in your shooting area with your shooting position. They ALL need fine tuning.

MVs..well as mentioned already..they are only as good as the equipment thresholds...but lets go one step further in that. The thresholds are then only as good as your shooting consistency. Browse the threads on MVs changing from shooting position changing

IMO Bottom line in firing solution calculations-----Trust Nothing, Verify Everything.

Sincerely,
Theis

In God we trust, all others bring independent, unbiased data to allow us to form our opinion.

 

[Clearlight]

Hi,

The great exterior ballistic debate of "Tru Dis, Tru Dat".

BCs are NOTHING more than a starting point. There is not a projectile manufacturer advertised BC out there that is going to match the BC you end up with in your rifle, in your shooting area with your shooting position. They ALL need fine tuning.

MVs..well as mentioned already..they are only as good as the equipment thresholds...but lets go one step further in that. The thresholds are then only as good as your shooting consistency. Browse the threads on MVs changing from shooting position changing

IMO Bottom line in firing solution calculations-----Trust Nothing, Verify Everything.

Sincerely,
Theis

Yup . Sometimes I like to demonstrate this by using an equipment change . Swapping from an Atlas V8 to an
LRA F class bipod will give a lot of folks different elevation. . The LRA usually impacts higher for most folks ,
much to their disbelief it’s as much as one minute at 500 . Is it you or the solver that needs truing ?

 

[viva la figa]

Yup . Sometimes I like to demonstrate this by using an equipment change . Swapping from an Atlas V8 to an
LRA F class bipod will give a lot of folks different elevation. . The LRA usually impacts higher for most folks ,
much to their disbelief it’s as much as one minute at 500 . Is it you or the solver that needs truing ?

I admit I am not a 100% accurate machine. But my main question is regarding the BC printed on the box. I am taking the stated value and trusting its accurate. I have not messed with the BC before in ballistics ARC so I was curious how much I should adjust by. All the other stuff you guys are mentioning is stuff I can work on personally to get better but I want to know my dope is spot on before I can eliminate those other variables

 

[Diver160651]

Given that the rifle data was then same and the weather was entered accurately why would my MV change from 2890 fps (checked with magnetospeed) and yet when the dope was trued up at 900 it said my MV was 3190

Generally, the number on the current boxes are very close, except for ultra slow loads..

Where did you shoot 900yards? My guess is that it is NOT 900 and you may of had a combination of other contributing factors.

Make sure all of your data inputs, rifle and weather are correct. I would go back first and shoot a zero the same way your going to true. Measure any offset, shoot 500y ish, true velocity if needed, then go the the 900, that is really 890 and remeasure your offset. Tune BC only AFTER you have done the first steps.

 

[Long Range 338]

Where did you shoot 900yards? My guess is that it is NOT 900 and you may of had a combination of other contributing factors.

^^^ This. It's easy to blame the shooter, scope, mounts, velocities, etc. Actual verification of range is a BIG one. It seems we have the tendency to trust distances that are given to us (maybe I'm speaking for myself only here). In my experience people have the tendency to round the actual numbers. "Yeah that one is 900" when it is actually 883 or something like that. When the numbers just won't line up and you have to throw everything out the window and start over by verifying everything is when I actually get that "ah-ha" moment.

 

[Diver160651]

^^^ This. It's easy to blame the shooter, scope, mounts, velocities, etc. Actual verification of range is a BIG one. It seems we have the tendency to trust distances that are given to us (maybe I'm speaking for myself only here). In my experience people have the tendency to round the actual numbers. "Yeah that one is 900" when it is actually 883 or something like that. When the numbers just won't line up and you have to throw everything out the window and start over by verifying everything is when I actually get that "ah-ha" moment.

I am pretty sure I know the range he used for 900 it's LOS is about 3° @ 890 and if out wind is really blowing L-R it can appear to need a BC fix as well.

 

[viva la figa]

Hahahaha yup at Avenal....890 it is.

 

[viva la figa]

Ok that makes a bit more sense. It is easy to round up. But at the match i had each stage mapped (the distances were listed (an unusual number like 438yrds not 450yrd) and i assumed properly ranged which I believe scott confirmed to be true if memory serves) and i plugged the exact mapped distances in and built my dope card for that stage.

 

[Diver160651]

Ok that makes a bit more sense. It is easy to round up. But at the match i had each stage mapped (the distances were listed (an unusual number like 438yrds not 450yrd) and i assumed properly ranged which I believe scott confirmed to be true if memory serves) and i plugged the exact mapped distances in and built my dope card for that stage.

I think you might have an offset, your velocity seems way to high to be true.

I might drive down Thursday your welcome to come out and confirm your dope

 

[viva la figa]

Shoot.....I'll see what I can do. Busy week but might be able to if I get my ducks in a row.

 

[pitdog85]

no one is mentioning the weather that cannot be controlled in this (mirage/heat shimmer)? here in the tropics I shoot across flat field temps are always 80-100F in American terms with high humidity. at 700m I usually have to add between .2 and .3mils to hit steel. That is a bigger error factor than any of this that cannot be calculated by computers.

 

[Dthomas3523]

no one is mentioning the weather that cannot be controlled in this (mirage/heat shimmer)? here in the tropics I shoot across flat field temps are always 80-100F in American terms with high humidity. at 700m I usually have to add between .2 and .3mils to hit steel. That is a bigger error factor than any of this that cannot be calculated by computers.

Gets hotter than that here. Back the power down and get off the ground.

 

[pitdog85]

Gets hotter than that here. Back the power down and get off the ground.

yes it gets hotter than that here too well over 110f in American terms my point was that its ALWAYS hot 80-100F all year round no such thing as a cool weather break where mirage backs off like you guys get in the states.

 

[RonboF117]

How reliable is the BC data printed on the Berger Bullets box? Is there a bit of "marketing" built into that number?

Given that the rifle data was then same and the weather was entered accurately why would my MV change from 2890 fps (checked with magnetospeed) and yet when the dope was trued up at 900 it said my MV was 3190

Hope this helps.

TRUING A ROUND. A technique I teach is to true at the longest distance possible, with that distance defined as where bullet velocity has dropped to 1.2M. This ensures laminar flow over the bullet just prior to the large drag rise that occurs in the transonic region. The bullet is predictable with steady state laminar flow versus the much more difficult to calculate area where turbulent flow exists and the drag is constantly changing. Once you have an accurate MV, use a trusted ballistic computer to compute the bullet speed at the distance 1.2M occurs. To quickly determine that speed, take your OAT (outside air temp in F) and add 1058 to it. This is where the bullet is supersonic. For example, let's use an OAT of 83F; 83F + 1058 = 1141 fps. Because that is 1.0M, we must multiply that number by 1.2 in order to determine 1.2M. Now that you have that number, look on your chart for the distance that matches that speed. Remember, if you have to err on one side or the other to match the target range you have available, err on the higher speed side. As an aside, you can quickly validate this formula by using it to calculate Mach under ISA conditions. 59 + 1058 = 1117. (That number is always easy for me to remember because I was a test pilot on the F-117.) . One last thing ... I have written in the past on why you should NOT use the number 1.2M = 1340 fps for truing that a lot of people hang their hat on. That speed is for ISA only (59F) temperature conditions. As any ballistic calculator will show, the farther away the temp is from 59F when you still use 1340 rather than the actual number, the greater the miss. For this scenario using 1340 fps rather than 1141 fps, in a sample 6.5CM it will equate to a 4.0 Mil difference in elevation and a 210 yard difference in range. © 2019 Copyrighted material, free use for non-commercial papers and publication. Approved for use on Sniper's Hide. Contact author for other uses. Ronald C. Evenson, Kinetic Ops, Inc.

 

[viva la figa]

That really helps. Why is the MV for 59*f different than the rest?

 

[Dthomas3523]

That really helps. Why is the MV for 59*f different than the rest?

That’s one of the parameters for sea level. 59 deg and 29.921 hg.

 

[Dthomas3523]

Relative humidity plays a part as well. But if I’m not mistaken, it doesn’t impact ballistic performance enough to matter like pressure and temperature do.

 

[viva la figa]

according to my ballistics calculator....If I shoot an innitial MV of 3011fps then only at 1590yards will the bullet speed drop to 1.2M or 1141fps. I dont know anywhere that I can shoot that far....I would have to go buy a muuuuuuuuuuuch bigger AR500 plate to hit out at that range!

SCREW IT....I am selling all my guns and buying a 22lr....how hard can it be! hahahaha (KIDDDDDING!!!)

 

[Dthomas3523]

That’s the reason most people don’t bring up the 1.2m. Most people don’t have access to range far enough.

That’s why <=600 for MV and 800 or 1k for BC is recommended. It’s about the most distance most anyone has access to.

 

[sobrbiker883]

wow.

A lot of great stuff here, and it makes my head hurt.
The OP’s questioning what happened from (maybe) 900 and in under match conditions yet doesn’t have a handle on DA shifts can affect his ballistics.

Back to basics: rezero rifle, get SOLID environmental data (DA is your best friend here), log real DOPE for known distances from a solid zero on paper to 1k, tweak whatever you like in your calculator (MV isn’t golden, I’ve had 3 Oehlers give me three different results) to match what you shot at KNOWN distances from 100-1k, and you’ll be within a tenth with a cheap ass ballistic app to as far as you can shoot a Creedmoor to in field conditions you’ll endure in a match.

The weak link is the loose nut behind the trigger, always.
Changing gadgetry to fit what you want to see (or whatever makes you warm and fuzzy) won’t change what the bullet is doing.

A smart but crazy guy down in Kingsville taught me years ago to above all else “believe the bullet”, and it unwrapped my head from axles ever since.

 

[viva la figa]

I'll be going back to avenal to do exactly that. I am tweaking my reloading process a bit to tighten up that area and improve consistancy. One big question is who is shooting 210 berger VLD Targets? What BC are you guys using in your calculators the published BC or one that you tweaked to fit what your dope was saying?

 

[RonboF117]

That really helps. Why is the MV for 59*f different than the rest?

59F is part of how ISA (Int'l Standard Atmosphere; 59F and 29.92 in.) is defined but as Mach is temperature dependent, so is your MV. Given the same altitude, your MV will change as the temperature changes. Temp up, MV up and vice versa. As you have a temp rise while staying at the same altitude, air density decreases so MV will go up. If you want to go further into the weeds, the temperature stability of your propellant makes a difference also, which can in turn, affect your MV. A technique used by many snipers at altitude in Afghanistan was to lay the loaded magazines out in the sun in an effort to raise the temp of the propellant to overcome the decrease in MV due to altitude change (MV goes down because OAT is less but you recover a good portion because of the density decrease). The newest mil ammo is very temperature stable so I don't think it is as critical these days (past couple years).

 

[RonboF117]

Relative humidity plays a part as well. But if I’m not mistaken, it doesn’t impact ballistic performance enough to matter like pressure and temperature do.

The second half of your statement is spot on. Humidity has very little to do with ballistics. Try running your calculations at 0% and 100% and you'll see essentially no change in the ballistic performance of the round. That's why many shooters, as a technique, set humidity at 50% for all calculations. For example, 6.5CM holdover at at 83F and 29.92 at 1000 yds and 100% humidity is 9.4 Mils/32.2 MOA. At 0% it is 9.5 Mils/32.5 MOA. Being off your wind estimate by 1 mph is the same as the elevation change difference btwn 0 and 100%. Low enough to be inconsequential. Set it at 50% and leave it. One less input to worry about.

 

[RonboF117]

according to my ballistics calculator....If I shoot an innitial MV of 3011fps then only at 1590yards will the bullet speed drop to 1.2M or 1141fps. I dont know anywhere that I can shoot that far....I would have to go buy a muuuuuuuuuuuch bigger AR500 plate to hit out at that range!

SCREW IT....I am selling all my guns and buying a 22lr....how hard can it be! hahahaha (KIDDDDDING!!!)

The point is to go to the furthest distance that you are both accurate and repeatable that still has clean air. That will give you the most accurate data when calculating a new BC. The 6 series bullets out of a 26-30 inch barrel is going to be way out there. However, take a standard .308 and you're looking at 950 yards for truing.