Ballistic coefficient G1 and G7

[hooksz86]

??? Im not sure on this. I guess the bullet goes to a G7 after dropping to a certain speed? Or maby the G stands for generation of BC math?

wikipedia- In ballistics, the ballistic coefficient (BC) of a body is a measure of its ability to overcome air resistance in flight.[1] It is inversely proportional to the negative acceleration —a high number indicates a low negative acceleration. BC is a function of mass, diameter, and drag coefficient. It is given by the mass of the object divided by the diameter squared that it presents to the airflow divided by a dimensionless constant i that relates to the aerodynamics of its shape. Ballistic coefficient has units of lb/in² or kg/m². BCs for bullets are normally stated in lb/in² by their manufacturers without referring to this unit.


I bet someone on here knows about this. So on the berger 338 300gr it is .818 and .419. So if the SMK is .768, what is its G7.

Sorry for the dumb question maby, but I bet I can learn better on here than I can other places on google i'v looked. Thanks guys.

 

[goober]

Re: Ballistic coefficient G1 and G7

In short some shapes match certain graphed flight patters better than others for example a flat based bullet compared to a boat tail bullet .The G7 curve in this example fits the boat tail bullet better than the flat base especially after 500 yard or so .
Bullets fly different and you G number fits some shapes better than others -I hope that helps and makes sense

 

[hooksz86]

Re: Ballistic coefficient G1 and G7

so what you saying is the G1 and G7 are two different styles of bullets or two different styles of BC measurements. Im not arguing with you but if im getting you right, why would they list the G7 or G1 if it is not the style of the bullet being described? Still a little hazy for me. Maby you can explain better.lol.

 

[goober]

Re: Ballistic coefficient G1 and G7

Read this -http://www.calguns.net/calgunforum/showthread.php?t=283567

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

For a very long time G1 has been the law of the land. While G7 was around for quite a while, nobody took advantage of it, Until Bryan Litz started crunching the numbers, because technically, as pointed out, G1 was for a flat based bullet and G7 a boat tail.

You can get to the same place with both numbers, though some will argue the numbers at the end the trajectory will be a bit better with G7 because the "model" is based off the (boat) bullets a precision shooter will use.

It's essentially saying a very similar thing in a different way, and how the average user would look at it is, the G7 figures as given to us by Bryan Litz are a "better average" designed to trace the bullets' projected trajectory from start to finish.

However in reality, since we have been using G1 for a very long time we have a ton of useful data which makes it just as effective, especially inside the supersonic range of the bullet's trajectory. Practically speaking, you do pretty much the same amount of work regardless of which model you use. Some might argue one over the other, but my experience, as well as too many years with a proven track record (G1) it doesn't really matter much, mainly because the ballistic programs do all the work and are pretty well versed in both. The rest is more of an academic exercise as the practical exercise plays out very close to the same.

So, if you have a G1, use a G1, if you have access to G7 numbers, use G7, it's not gonna change things enough in most cases, unless you really need a super accurate approximation of the transonic region or what the bullet might do beyond that barrier, that is where the work put in by Bryan shines.

It's six and one half really... G7 is a good average, and most will say to get the same results you want to adjust or step the G1, however I found both work equally well, adjusted, stepped, etc.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

To toss a bit more on the fire,

While Patagonia Loadbase 3 doesn't use the Point Mass solver that G7 tends to work better with, here is an example of an comparison between G1, G7 and Doppler Radar with a 338LM (250gr)

As you can see it is too close to call across the board. Some programs do a bit of a better job than others, but still when it washes this close you have to call it as you read it.

 

[Graham]

Re: Ballistic coefficient G1 and G7

I've never used G7, and the bullets manage to go where the rifle is pointed, even when transonic.

 

[Fred_C_Dobbs]

Re: Ballistic coefficient G1 and G7

Understand that BC isn't a "real" property, at least not like mass or temperature or height. It's something that was made up by shooters so they could use a slide rule to aid them in predicting where the bullet was going to go before they'd pulled the trigger. So whatever terms we use to describe a BC are every bit as "made up."

We think of artillery as something that gets shot at unseen targets from many miles away, but that wasn't always the case. Before the War Between the States, an artillery piece was nothing but a very large rifle (or musket), and the gunner only could shoot at targets he could see. Until a Confederate corporal (and child mathematical prodigy) demonstrated that he could employ triginometry to calculate a ballistic solution to shoot at and hit a target that he could not see, shielded by the hill that stood between them, simply by lobbing the shell over the hill at a precisely calculated angle.

This obviously would give any military a huge advantage over an an opponent who could only employ artillery in direct fire mode. So military minds the world over became obsessed with the idea of exploiting the concept of indirect artillery fire and developing it into a combat effective tool. But for that to happen, because of the extremely long paths of flight that would involve, they needed to be able to predict with a high degree of precision the rate at which their artillery shell's velocity would bleed off because of aerodynamic drag.

One of the products of that research was the G1 drag model standard shape. The "1" was simply because it was the first of the many models they expected to create. The "G" was in honor of the Gavre Commission, a goup of French ballistic pioneers who had been instrumental in founding the new science. So that's all that "G1" means.

G1 was a mathematical representation of a standard late 19th Century artillery shell, which had a low ogive number (~2) and a flat base. It's no coincidence it was so similar in shape to the Minié ball (except the artillery shell lacked the Minié ball's cannelure and concave base): they were designed to operate over roughly the same range of velocities.

The G7 model largely was a byproduct of the invention of smokeless gunpowder. Where black powder projectiles didn't go that much faster than the speed of sound, smokeless propellant was capable of driving bullets to well more than 2000 fps. And that was where the G1/Minié ball shape fell short. It bled off energy too quickly at such high speeds, which made it too "inefficient." So to take better advantage of the new gunpowder, they created sleeker bullets, first with pointier noses and later with tapered "boattail" bases. Which was great for conserving energy and extending the round's useful range, but its speed no longer decayed at the rate predicted by the old G1 models. So as the shape of the high speed, long range bullet evolved, they kept having to create new drag models to better represent the performance of the new bullets' shapes.

Fr. Frog's web site has sketches of several of the prominent G model shapes.

 

[calling4life]

Re: Ballistic coefficient G1 and G7

Maybe we pin this to the top?
Some worthwhile info for all and with these terms being thrown around on a regular basis, this would be a help to those just stepping in to this sport.

 

[hooksz86]

Re: Ballistic coefficient G1 and G7

Ok, I think I understand this a lot better now. As far as me entering a BC into my sierra external balistics programe, I should still use the G1 BC since it seems to match up with my clicks for actual paper at the house. But if I were to finish the math on the G7 as stated above it would be about the same as the G1 or maby a little better? thank you guys very much for taking the time to type this out.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

Here is a brief explanation of the facts:

http://02b0516.netsolhost.com/blog1/2009/06/17/a-better-ballistic-coefficient/

<span style="font-style: italic">CAN</span> you calculate long range trajectories with G1 BC's for modern (boat tail) bullets?

yes.

<span style="font-style: italic">CAN</span> you drive a nail with a crescent wrench?

yes.

Insisting on using G1's for modern long range applications is like insisting to drive nails with crescent wrenches, when you also have a hammer.

There are those who will say: "either way the nail gets driven, so, there's no difference". To each his own. I use a hammer for nails.

-Bryan

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

Go to Home Depot, there are 10 different kinds of Hammers a person can buy. To say that prior to Applied Ballistics everyone was unsuccessfully - successfully using a cresent wrench is bit misleading.

It's really more like using a lighter hammer on a framing nail, or a very heavy hammer on a finishing one. Many people couldn't tell the difference.

The G7 data is very new, and the G1 too well established, in some cases there are no G7 numbers, and in others there are years of successful history. The difference is, back then nobody was commercially invested as they are today. Everyone produced data based off the G1 standard as it was the only game in town. In that time we saw an awful lot of success by a variety of shooters across varying conditions.

When given the choice, with a Point Mass solver I opt for G7, but I've never had G1 let me down as far out as 2000m. In some cases unfortunately the G7 is just not available. The bullet does not fall out the sky using a G1 model.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

You're right, there are many kinds of hammers.

Here's the G1 hammer:

Then there's the G7 hammer:

You have a point that if there's no G7 BC available, or if your software doesn't support G7, then you can 'make do' with G1. But given the choice, G7 is the better option.

Yes there were successful long range shooters before the G7 'paradigm'. There were successful long range shooters before optics, smokeless powder, jacketed bullets, etc. There were even successful long range shooters before Snipers Hide

The point is that the G7 approach to computing ballistics is better for modern applications. Given the level of sophistication of all our other modern equipment, the difference is actually noticeable. If a shooter is serious enough to invest big money in a custom rifle, several $1000 optic, laser rangefinder, chronograph, etc, everything to maximize first shot hit potential at long range, it's just not consistent to use a G1 based trajectory prediction.

Many average home owners might not know the difference between different carpentry specific hammers, but carpenters do. Likewise many average shooters won't know the difference between G1 and G7 BC's, but careful long range shooters do.

-Bryan

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

I don't disagree... But it is hard to see it when the numbers are within a minute and you still haven't' shot it... academic as I said as the practical reality is, G7 is not always the closest to right answer.

Here is data straight from JBM with your G7

Here is the same exact data with G1

It is 1 Minute off each other at 1100 yards...

The difference here and I think it is important...

Your numbers are "HIDDEN" as they are in a lot of the software. The G1 is readily available. I have discussed this before, when a person needs a point of reference it's not available. So unless they "buy" the book, the software regardless of how robust is not helping the shooter. Unless of course they use G1.

G1 is known because it is out there in the public domain. Like SH we give out as much information as humanly possible. We don't hold any of it back knowingly.

Still, 1 minute, and when the guy shoots it, who knows were the actual number will fall. Could be smack in the middle, 1/2 minute high of G1 and low of G7 making it a wash. So obviously, I mean we can see, the software knows how to handle both. Not always about what you say, but what you can actually show. As I have demonstrated in more than one post.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

What I get from your post is:
11.5" (1 MOA at 1100) of error is unimportant,
and SH shares information freely while I don't.

You're taking us off topic, but I'll bite.

First, if your actual POI is 1 foot different from where it's predicted, there is something wrong with your inputs. The G7 is the closest to reality and if your actual POI falls closer to the G1, then there is some other error in the system which is offsetting the G1 error. Maybe it's just wind. It's like saying if you have enough sources of error then individually they're less critical. If you know that G7 is better suited than G1, why use the G1? Is it too expensive? Does it cause you physical pain?

As to the money side of it; SH has material you can see for free, and material you have to pay to see (training). Hiding the G7 BC's in the ballistic programs is no different. You can use the number, but if you want access to the list of numbers, get the book.

Apologies to the OP for going off topic. G1 vs G7 is not a political or popularity contest. It's science.

-Bryan

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

As I stated,

The G7 is not "always" the correct answer when practically shot. You have no way of knowing which is correct, so the idea you put forward that it matters is simply academic ... practically speaking you have no way to know where the individual bullet will strike and whether the G7 solution is "better" than the G1. Working off averages in a model you designed has some bias.

I said, I agree regarding the idea behind it, and that given the choice I clearly stated I tend to use G7. So skipping all that, when there is a financial interest in making something "appear" more right than wrong, well, again the numbers don't lie and the practical reality is not always as simple as you make. you have a vested interested in making everyone believe G7 is right and G1 is completely wrong.

yes I charge for training on here, but don't go around telling everyone that the SH training is the best training they can get and if they use something else they are wasting their money. Like you said, it's a 1 MOA at 1100 yard difference but an important one. You'll notice that companies that provide training are not required to be Commercial Sponsors, hence they are not charged to compete against the SH training program on here.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

We can let go of the business discussion now and just agree that we both work in the shooting industry.

But I do want to address the original topic. I think you're on to something that's important to explore.

It's easy to show that the G7 drag model is a better fit to the drag profile of modern long range bullets. I don't think anyone disputes this.

Now compute a G1 based trajectory, then compute a G7 based trajectory and go out and shoot.

The observed POI will be somewhere in relation to the G1 and G7 predictions.

Now here's the critical thinking part.

If the actual POI is closer to the G1 prediction, does it mean that the G1 drag model is actually right for that bullet?

Discussion:

* We <span style="font-style: italic">know</span> that the G7 model is a truer representation of modern bullets.
* We have observed a bullet POI being closer to the G1 prediction in a specific case.

Considering the above statements, there are two conclusions we can come to.
1) we change our mind about G7 being better and decide that the G1 must somehow be better for this bullet. This is the conclusion you and some others will want to come to.

2) The alternate conclusion which I find more likely is that there are other errors/uncertainties in the ballistic calculation which are unrelated to BC that are responsible for the error between G7 based prediction, and observed reality.

To amplify the idea, let's say you're comparing two methods of predicting trajectories:
* a G7 based solver, and
* a lotto machine (you know, that spits out the balls at random)

Now lets say the G7 solver tells you 9.8 MILS, and the lotto ball is 10, and you actually used 10 MILS. Would you conclude that the lotto machine is a better predictor, or would you conclude that the lotto machine just got lucky?

The problem is that in the real world, the G1 and G7 predictions are often close enough that the difference between them is 'in the noise' of most shooters ability to measure all the other variables, etc. But just because it's in the noise, doesn't mean one isn't still more 'right' than the other. (This is the same argument we have about using scope levels) Said another way, just because one is right by an amount that's easily masked by other unknowns, doesn't mean it doesn't matter that it's right.

If there's great uncertainty in your shooting, eventually everything is 'in the noise'. Like if you're not using a rangefinder but estimating range with a reticle it will probably matter very little if you're using G1 or G7. But the closer you get to nailing down all the variables, the less gets lost in the noise.

-Bryan

 

[Jackem]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ch'e</div><div class="ubbcode-body">Read this -http://www.calguns.net/calgunforum/showthread.php?t=283567 </div></div>

Thanks for the link. As the majority of my shooting knowledge is dated by about 10 yrs I'm amazed on how the science of shooting coupled with range finding technologies has changed how far is too far.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

Head you Win, Tails I lose....

Sorry I was at the range actually shooting stuff, and by some miracle of luck managed to stay within my consistent 1/2 MOA at distance. Noise ratio was low today.

Lotto Machines now, that is what everyone who used G1 prior to Applied Ballistics was doing, getting lucky.

Sorry, I don't' follow the logic that if using the same program over and over, and it gives you useful, practical results, over and over, how that is luck ? The fact the military, the datebooks, the ballistic cards all written prior to 2009 were not much more than throwing dice or dropping a lotto ball seems a bit strange to me.

I just don't see how a program, any program that is capable of using both G1 and G7, when giving the data is some how overly flawed if you use G1, that just doesn't' hold true out on the range, in reality. That if the information is right, it's actually wrong, really, that is the logic ?

I get it, being a friend is probably politically and professional smarter, but when it doesn't make sense, it's hard to cheerlead one set of numbers over the other. Especially given the much longer history, let alone the actual downrange results.

Have a great day, I have a video too edit...

 

[THUNDERBOLT68]

Re: Ballistic coefficient G1 and G7

TAG

 

[hooksz86]

Re: Ballistic coefficient G1 and G7

So, hey Brian, Im the guy that e-mailed you yesterday on this question. Im glad to see that you can explain yourself very well. Im guessing you help design bullets for berger? Im enjoying this listening to you guys talk/debate this topic. I guess we just need to get a guy from Sierra and Lapua on here too.lol Im learnin a lot though. Thanks

 

[RemingtonSPS]

Re: Ballistic coefficient G1 and G7

I have experience using Nightforce Exbal and Shooter ballistic programs only. Here is my personnal experience based off of what i have seen with the two programs and using one BC in G1 and G7.

Exbal (G1)
In my experience using Exbal (it only uses G1 BC's) when i tried to input one average G1 BC it would be on at mid ranges (5-600yds) and off at longer ranges (1k+). You could correct this by doing a Trajectory Validation but that only changed the Muzzle Velocity and not the BC. The only way i could get it to match my bullets actual trajectory was to use the Multiple Ballistic Coeffecients and manually tweak the velocity and BC's until it was as close to perfect as i could get it.

Shooter (G7)
Shooter allows the input of one BC in G1 or G7, or the use of multiple G1 or G7 BC's. BC numbers are usually based on an average over a specific velocity range, whereas the actuall bullet BC is more dynamic and changes with velocity. I found when using one BC the G7 profile tends to be initially closer to my trajectory than the G1.

That is only my personnal experience, i will leave the numbers games and the which is better debate to the more educated.

A friend of mine tested a program a few years back. He said that it "automatically degrades the G1 ballistic coeffecient" and that it was incredibly accurate even out to longer ranges. I have no experience personnaly with it but he did say he prefered it over Exbal at the time.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

Exbal is a bit outdated, and Gerald Perry has visited Rifles Only on several occasions when I was there, and we sat down with him on more than one of these occasions to discuss the program and the ballistics. Currently despite being asked, has refuses to use G7, and I know several have requested this change.

I have every program currently available I can think of, from FFS to Shooter, and everything in-between to include NF Exbal, and they all output slightly different, as well as offer a variety of features to help the shooter validate the program. It's important to calibrate the system for the best performance and in my opinion, as recently as last month have shoot using these programs to include the use of G1 to 2000m. The results downrange on UKD targets was accurate and predictable.

As noted and ignored above, Patagonia Ballistics, which is a foreign based Ballistic Expert, uses a different model than most other software. He deviates from the more common Point Mass Solver, where G7 tends to do better. In that I have posted the spread sheet that clearly shows BOTH G1 & G7 as compared to Doppler Radar Data, it is easy to see how both stay within acceptable ranges alongside the Doppler Radar Data. It doesn't get any better than having Doppler Data and the fact they trend equally alongside one another is hard to argue with.

Fortunately for everyone, we are not using Lotto machines to predict our trajectories, and because we have reams of data prior to 2009, these programs, many of which were available prior to G7, do a very good job of predicting where the bullet will land.

There are other ways to calibrate besides adjusting the MV, you can manually edit the BC, I routinely adjust the BC using the Utility in Bulletflight based on my actual drop. Field Firing Solution for instance used a DK Factor to retard the flight characteristics of the prediction to better match your final output. At Gunsite during the XLR class we spend no less than 2 days gathering data to calibrate the software so that it will match at distances beyond 1000 yards.

We also tested software alongside one another, using Ballistics FTE with G7 and Bulletflight with G1 and Bulletflight was noticeably more accurate this way. We tested it out to 1000 yards actually being shot. So while anecdotal data is all over the map, that proves that this not as cut and dry as one being better than the other. Doppler Data is the most accurate, when your software trends alongside it with both G1 & G7 that says the sophistication of the software can easily overcome any downside inherent to the paradigm.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

The LB software is a 'one off'. It doesn't use a standard solver, which means that no commercially available standard G1 or G7 BC's work the way they should with it. For example, if I'm reading your screenshot right, it's showing virtually no difference between it's G1 and G7 traces. How can that be? How is it morphing the standards in a way that they're both the same? Whatever it's doing is not what's intended when a G1 or G7 BC is measured and assigned. Call it a custom representation or something, but calling it G1 and G7 is simply not true and will be of little use to those with actual, accurate G1 and G7 BC's. Those with actual, accurate BC's which are properly defined and capable of predicting accurate trajectories with standard solvers will get different results with LB. They'll have to reinvent the wheel around this 'one off' solver that morphs BC's into something else based on a single radar track. If that's you're cup of tea, that's fine. I'm about providing standardized solutions that work for everyone the same.

And here's a question. Is LB so good that it matches the limited radar data that well, or could it be that the entire LB solver was tweaked and bent around that one radar trace that you always love to show. I'm not asking to be a smart-ass, I really don't know but it looks that way to me. It makes a good commercial, if you don't know about these things. I'll bet if you looked at some radar data that was not available during the development of LB, that the comparison wouldn't be so favorable.

And you didn't address the critical thinking exercise. Does the fact that an observed impact is closer to a G1 prediction mean that G1 is necessarily *right* in that case, or could it mean that errors offset and made it look that way? I would truly like to understand the thinking here because I've heard this argument many times.

False conclusions are drawn from genuine observations all the time, but that's something to be avoided, not advocated.

-Bryan

 

[Bearwalk]

Re: Ballistic coefficient G1 and G7

I'm not sure you and LL are alwys arguing apples to apples and may be why you guys never seem to get settled on this issue. It may be G1, it may be G7, or something else entirely....

I use three different <span style="font-style: italic">drag functions</span> types (note, not BC)- G1, G5 and G7 depending on the projectile I am using. For example, my data shows that only SMKs and VLD type bullets do well under the G7 profile. SGKs are best approxiamted by a G5 profile and almost everything else is best approximated with G1. These are broad brush strokes, of course, but demonstrates my point that the proper, or best, drag function is determined by the bullet profile and borne out by field results.

Why limit ourselves to one drag function type as the "best"? Use'em all I say.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">

And you didn't address the critical thinking exercise. Does the fact that an observed impact is closer to a G1 prediction mean that G1 is necessarily *right* in that case, or could it mean that errors offset and made it look that way? I would truly like to understand the thinking here because I've heard this argument many times.

False conclusions are drawn from genuine observations all the time, but that's something to be avoided, not advocated.

-Bryan</div></div>

How can 50+ years of history be a false conclusion, especially when repeated as often as it is... you appear to be coming to this from the point that any positive results using the G1 paradigm is an accident, that the bullet just happens to intersect in the same place out of luck.

I get it, the model is based on the idea of bullet types, but if this was the case, why wasn't the G7 standard used sooner, like in the early 80s when the military moved to the boat tail rounds, especially in sniping ? Certainly they knew about the G7 back then, so why did it take to the mid 2000s to make the case ? Unless the bullet and the G standard is just not that sensitive to each other as one might think... they can be much more forgiving rendering either model equally effective.

We had computers, ballisticians, ballistic software, heck even rocket scientist working for the government in a similar capacity, yet, they continued to produce data using the G1. G7 was there, yet unused for a long, long time.

Admittedly, I am not a scientist or ballistisan, so I have no way of knowing if the G1 being used is as absolute as pictured above or if it was modified from the original definitions, <span style="text-decoration: underline">but it does work</span>. And beyond the limits of what I would call an accident. Possibly the curves are much less dynamic and the trajectory course enough to fudge.

If you are hearing this same question many times, i would certainly take that as a clue. Especially with all the practical experience behind the G1. It's hard to argue with results let alone the history of its use.

<span style="font-style: italic">I don't have a real answer,</span> I can't say it is not an accident from a scientific standpoint as I am not equipped to think that way. What I do know is what my eyes tell me to include the results observed since 1986 when I graduated Sniper School. I have been shooting a very long time and hitting my targets almost as long. I have never crunch a number based on a math formula someone else wrote way too many years ago in order to determine the flight of the bullet. To say everyone who gave us a G1 BC for a modern bullet is wrong, I find a bit hard to swallow. But I don't' doubt it is possible based on the direction I think you are approaching it. However the world does not work that same way, the world is an "IF" - "THEN" proposition, if I do this, then this happens, in which case G1 works the same exact way as G7 in most cases.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

In reference to Loadbase 3,

The data was off the shelf so to speak and not bent to fit a curve. The whole process was written about by the author Gus R from Patagonia over at LRH, and the article can be read following this link.

http://www.longrangehunting.com/articles/ballistics-predictions-1.php

One note from the article:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">It is pretty noticeable, as expected, that the Point Mass method is quite reliant on the selected Drag Model, a fact that was proven by many tests. It’s not a criticism of the method itself, since there is nothing wrong with that. But, that makes the Point Mass method not very practical, since when not coupled with the right drag model, accuracy can deteriorate significantly.

In contrast, the LoadBase 3.0 ballistics engine shows its flexibility by accurately handling either G1 or G7. Check the almost indistinguishable curves. Therefore we can say that the engine is not drag-dependent since its accuracy is not affected by the selected drag model. </div></div>

This tells a similar story to the one I believe I am telling... no fudging of the data required.

So to go to the question asked earlier, if G1 matches up is it just a wrong answer that hit right or is the problem within the software itself or the modeling ?

 

[hooksz86]

Re: Ballistic coefficient G1 and G7

Ok, so I can see where both are coming from. I read the G7 article by Bryan. The G7 makes sence to me that when Im using the bullets that im using. Witch is always a SMK or the berger for either my F/TR 308 or 338 110ba, either the 168gr or 300gr. Now with my other rifles im not shooting far enough to even need a program to shoot well. And yes my dad shooting sharps 45-70 lead 520gr bullet, the weight of bullet overcomes the shap or drag of this that style of bullet.
So using the G1 obviously works ok or probably good enough to get in the ball park for sure. But if there is math out there that will do better for longrang(1100-2400yards)boattail long ogive bullet then that is what I want to use. I have not used the G7 yet but want to or at least try it out.

So that being said, does anybody know how to or have any experience using the Sierra exterior ballistics program, the CD rom version? There is an advanced button on the custom bullet creation. It has 1-5 ballistic coefficients to put in and 1-4 velocity boundaries to put in. But I do not see any place to make sure it is using G7 and not G1. Im sure if I just enter in .419 instead of .818 for the 300gr berger then it is just going to make it look like crap. or in other words, I know the real poi will not match what I put in. And maby this program just will not be able to use the G7 math.

So does the G7 basically take into consideration the bullet slowing down and making the BC go down on the way to target? And you use the G7 because the G7 style bullet does not slow down as fast or the same way the G1 style bullet does? Am I thinking right on this? Oh and if the BC G1 is higher than another bullets G1, then I would think the G7 is also higher for buying $$$$ resions on picking wich bullet to shoot.
Hope you guys can help me some more with this even though you have already been a great help

 

[KYpatriot]

Re: Ballistic coefficient G1 and G7

I dont think anyone is arguing the G1 standard is ineffective...the argument is that it isn't the most accurate model to use. If we agree that we should do everything possible to be consistent and minimize errors then using the G7 standard when it is available seems to be the sensible thing to do. No one denies that spin drift is real even though for many shots it is "in the noise." But, since it is easy enough to account for, what would be the downside to including that effect in the solution? The more precise the weapon and shooter, and the longer the shot, the more important it would be to include SD right?

In the same way, concerning drag modeling, the G7 form clearly is a more accurate model for most of the bullets we shoot for long range, so if the ballistic coefficient data for that model was collected accurately, then the predicted BC must be closer to the actual BC. All other things being equal, it follows then that the solution must be closer to reality, in the same way that including spin drift puts you closer to reality. If we observe on a shot that it is not, then either the G7 data collection was inaccurate, or some portion of the shot solution other than BC such as the vertical wind gradients or inconsistent scope clicks or a dozen other variable or combination of variables is the cause.

We should also consider the possibility that the manufacturer published G1 numbers have been "tweaked" or adjusted to more closely match the real world results of so many shooters using that standard. If that helps, then we have mitigated the slight weakness in the G1 model. The point going forward though is...when a new bullet comes out, if we have both G1 and G7 BC data, then there is a compelling argument to use G7, even if for many shots the difference on the target may be lost in the noise. I would think the better the shooter and equipment the more often the benefit of the G7 model would be apparent. For shooter like me I'm not sure I will see it often, but I might as well take out all the error I can...

 

[Helmet]

Re: Ballistic coefficient G1 and G7

A bullets G1 is altered more dramatically by velocity than the G7. Why not use the model that offers a more consistent number throughout it's flight? I see Hornady is beginning to use G7 numbers in addition to the G1.

 

[gstaylorg]

Re: Ballistic coefficient G1 and G7

Am I going to have to separate you two?

 

[milo 2.0]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gstaylorg</div><div class="ubbcode-body">Am I going to have to separate you two?

</div></div>

WHY??
Arguing with Mr Litz would be like pissing in a fan.

 

[gstaylorg]

Re: Ballistic coefficient G1 and G7

I know. It was meant to be humorous.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

Apparently nobody reads anything and just goes with the gut...

As noted in the link I provided,

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> In our example, the Pejsa’s method is a better technique than Point Mass, since even using the G1 drag model, it exhibits less differences. </div></div>

Maybe it is not the model but the method, also note the information regarding Patagonia LB3, which also follows a similar curve regardless of the drag function used.

 

[RemingtonSPS]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">is the problem within the software itself or the modeling ?

</div></div>

Great question! I think you're correct, the software differences is where the problem is at. That can be the only explanation if shooting the same rifle/optic/ammo and getting two different trajectories, from two different programs, using the same G1 BC. Whether you put in a closer fitting drag model or the program corrects the path for you, what difference does it make?

At the end of the day i only care about the program matching my trajectory, and if it doesn't i want the features built in to adjust it until it does.

 

[RTO]

Re: Ballistic coefficient G1 and G7

I figured I would stoke the fire a little. I see both points made by both sides. I agree with LL's point that if it gets a hit whats wrong with it? I will say I do prefer to use G7 and it never has failed me. I believe I am understanding your point Bryan but if you wouldnt mind clarifying for myself and others. When you say that G1 is wrong or not the best option are you reffering to G1 solely based on the single number and calculation used without a program doing any type curve adjustment and G7 number based on the number and single calculation without adjustment. What I am getting at is that you are saying G1 can not come up with the correct numbers even though these programs are coming up with what seems to be very similar or even potentially closer numbers to reality in some instances, OR are you saying that these programs are using other calculations to make up for the lack of G1 reliability for the newer boat tail type bullets to get a correct output?

I see both sides points and appreciate the debate.

 

[Augustus]

Re: Ballistic coefficient G1 and G7

Using G1 I have to tweak the BC at longer distances to match the trajectory, I was under the impression the G7 model helped to alleviate this.

 

[milo 2.0]

Re: Ballistic coefficient G1 and G7

I honestly think that this site has no regard for Bench Rest shooters.
Where did all of our knowledge come from.
The bench rest community.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

I still tweak my G7 number, depends on the rifle i use, for example, my Valkyrie needs the average tweaked. Instead of using .243 for the 175gr SMK, I use .239 most of the time.

For the G1, I found the stepped numbers to be quite good, as noted in the JBM image here, they automatically step the numbers for you so there is no extra work, you just pull the bullet from the library. The non-(Litz) entries tend to be stepped when available which does wonders for the final output. I believe you can step the G7 too, and Bryan has spoke of this practice in another thread.

 

[ctressler]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">academic as I said as the practical reality is, G7 is not always the closest to right answer. </div></div>

How do we determine what the right answer is?

Actual shot data is a really good start, though I've observed that many of the variables required to model the exact behavior of a projectile are not always determined with the same intensity and precision as that used to obtain the actual shot data. Therefore, when the model doesn't line up with the "right answer" things are tweaked until it does. Many shooters get by with this method just fine, most of the time.

To take full advantage of the difference between the G1 and G7 models, the variables need to be nailed down to a degree of precision and accuracy that eludes many. The ultimate goal here is to get first round hits with data we obtain from our software. The closer our inputs (variables) are to the actual correct value, the closer the software can model what is determined with actual shot data. As hard as we try, there are still going to be things that are difficult to quantify, such as the effect the angle of the sun plays upon point of impact on a cloudy day.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

Clearly you're not paying attention as demonstrated that the software used is the biggest variation which is beyond the end users control.

Point Mass Solvers favor the drag function, Loadbase and Pesjas do not favor one drag function over the other.

You also missed the part about having every program available, as well as calibrating my software and shooting. Note the example of spending two days at Gunste last month just to calibrate the software. Then all shots taken were on man sized UKD targets out to 2000m, most of which were camouflaged. That is only one example given, forget the fact I normally shoot 3 days a week every week.

Please, spare me.

 

[ctressler]

Re: Ballistic coefficient G1 and G7

LL, You said it yourself, your a shooter not a scientist yet you wax on like you know it all. Did it occur to you that my post was for the original poster of this thread, which you have highjacked.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CTressler</div><div class="ubbcode-body">LL, You said it yourself, your a shooter not a scientist yet you wax on like you know it all. Did it occur to you that my post was for the original poster of this thread, which you have highjacked.</div></div>

Maybe you should read on, did it ever occur to you that I might talk to people involved in this stuff... Forget the experience factor, I actually go out and practice what I preach.

Unlike most of you, I am Bi-curious and will explore both sides of a debate, in as much detail as I can muster. That includes digging for answers instead of blindly following, you'd be surprised.

When you own the pixels you can't hijack something, so if you don't like the direction I have taken, simply log out, or find another thread to stick your nose in.

 

[THUNDERBOLT68]

Re: Ballistic coefficient G1 and G7

It might be Hi jacked,
But I have learned a great deal reading this.

I bet the original poster did not realize he was getting this much value

 

[Country]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: longdistance</div><div class="ubbcode-body">??? Im not sure on this. I guess the bullet goes to a G7 after dropping to a certain speed? Or maby the G stands for generation of BC math?

wikipedia- In ballistics, the ballistic coefficient (BC) of a body is a measure of its ability to overcome air resistance in flight.[1] It is inversely proportional to the negative acceleration —a high number indicates a low negative acceleration. BC is a function of mass, diameter, and drag coefficient. It is given by the mass of the object divided by the diameter squared that it presents to the airflow divided by a dimensionless constant i that relates to the aerodynamics of its shape. Ballistic coefficient has units of lb/in² or kg/m². BCs for bullets are normally stated in lb/in² by their manufacturers without referring to this unit.


I bet someone on here knows about this. So on the berger 338 300gr it is .818 and .419. So if the SMK is .768, what is its G7.

Sorry for the dumb question maby, but I bet I can learn better on here than I can other places on google i'v looked. Thanks guys. </div></div>
Better late than never .

Drag Function Conversion
Input Data
Ballistic Coefficient: 0.768 G1 Caliber: 0.338 in
Bullet Weight: 300.0 gr

Velocity: 2300.0 New Drag Function: G7
Output Data
Speed of Sound: 1116.4 ft/s Mach Number: 2.060

CD of Standard G1 Bullet: 0.585 CD of Standard G7 Bullet: 0.295
Form Factor of G1 Bullet: 0.488 Form Factor of G7 Bullet: 0.971

New Ballistic Coefficient: <span style="color: #FF0000">* </span> 0.386 G7 <span style="color: #FF0000">* </span> Sectional Density: 0.375 lb/in²

 

[one shot ST]

Re: Ballistic coefficient G1 and G7

G1 and G7... I've seen people say..I'm using G7, better...but all the other parameters was out of control...

error measuring muzzle velocity, poor standard deviation, use of station pressure with altitude.... ecc ecc......

 

[KYpatriot]

Re: Ballistic coefficient G1 and G7

LL and BL,

As you both have said there ARE specific reasons why ballistic computations don't match reality...it is either in the error of the BC itself, or applying an imperfect BC model, or error in the algorithms of the solvers, which we know is true to some extent since different programs give slightly different results, and finally the error in estimating the environmentals which is likely our largest source of error if we discount shooter mistakes.

If we are going to nail down the errors in the solvers or the BC modeling then we would have to control the larger sources of error in order to produce valid data truly ferret out the reasons why these discrepancies exist.

So, have either of you ever heard of, or could think of a place that you could shoot a thousand yards environmentally controlled? It would have to be an underground tunnel of some sort, perhaps in a mine or at a base built during the cold war with connecting tunnels. I have been in one of these that would be long enough but it was filled with old supplies.

Imagine the kind of exact data you could get without ANY wind with the airhandlers turned off, an exact and consistent temperature, shooting from solid fixed position. Even if it had some slope, that could be measured and accounted for.

Would be difficult to set up and execute such a test, but I think it would be really informative and advance the algorithms in these programs.

 

[Country]

Re: Ballistic coefficient G1 and G7

Has anyone had any experience with the Apple application , JBM Ballistic FTE . I can't seem to find anyway to save a custom bullets BC and velocity data. The supplier of the application does not return any contact .
I spoke to the apple shop in my area and they did not even know the app existed. Great service!

 

[Mister Ouchie]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Country</div><div class="ubbcode-body">Has anyone had any experience with the Apple application , JBM Ballistic FTE . I can't seem to find anyway to save a custom bullets BC and velocity data. The supplier of the application does not return any contact .
I spoke to the apple shop in my area and they did not even know the app existed. Great service! </div></div>

Once you calc the trajectory you can save it as a "favorite" (upper right button I think).

 

[hooksz86]

Re: Ballistic coefficient G1 and G7

anyone have experiance with the sierra extieror ballistics program, cd rom?