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Berger Bullets' Move To The G7 Standard BC By Bryan Litz

 
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  #15  
Old 08-19-2009, 07:59 PM
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Re: Berger Bullets' Move To The G7 Standard BC By Bryan Litz

Hi Kevin,

As always, thank you for your support and clarification.

I went back and re-read the part about how/why we were stuck with G1 exclusively for so long; I may not have been entirely clear and I apologize for that. I agree with you that marketing is not the original reason for bullet makers using G1. I was just saying that marketing is a big part of the reason it has been and will be difficult to move to a different standard (because no-one wants to see their BC's numbers go down, for any reason).

We are in agreement, I just wasn't clear in my original piece. Thanks for setting it straight.

Regarding the idea of using many different drag standards...

It took me a little while to find it, but below is my answer to another shooter who asked about using G5 instead of G7. My response to him is pretty much the same as my response to your suggestion of using many different standards.

Quote:
It's true there are several other standard projectile shapes other than G1 and G7. It is possible to define a BC for any bullet in relation to any of those standards. Ideally, from a technical point of view, you should choose the standard that exhibits the least variation. For long range bullets, G7 is much better than G1, but in some cases, G5 can be a slightly better match than G7.

To put it in perspective, using G7 referenced BCs will usually erase 90% of the velocity dependence of a G1 referenced BC. In some cases, a particular bullet may have an additional 5% improvement if referenced to some other standard (like G2, G5, etc).

Although it may technically be a better solution to use G5 in some cases, I offer the following arguments against that practice:

1. If you start using many multiple standards to define BC's, you loose the ability to compare bullets based on BC. For example, if 'bullet A' exhibits a slightly better match to the G7 model and it has a G7 BC of .237, and 'bullet B' exhibits a slightly better match to the G5 model and has a G5 BC of .342, you can't say which is better based on BC (not without converting, which is a lengthy and complicated process to do right). My point is that it's better, from a standardization point of view to adopt one standard rather than using multiple different standards. You're still eliminating most of the velocity dependence by using the G7 standard.

2. The experimental data isn't always good enough to determine which match is better. My experimental data is very good at generating a reliable average BC (regardless of the standard used). However, the variation in BC, which is determined from the exact shape of the drag curve, is much harder to nail. So if you have a bullet with 0.006 variation in G7 BC and the same bullet has 0.010 variation in G5 BC, can you say for certain that the G7 is a better match? Not with my data. My data is good enough to resolve that a G7 (or G5) BC has much less variation than a G1 BC because the difference is so huge. However, the difference in the shapes of the drag curves between G7 and G5 is so subtle, and honestly, my data isn't good enough to say for sure which is a better match for each bullet. Naturally, since the difference is small, it has a minor effect on the accuracy of the trajectory you'll calculate.

You may notice that the above 2 considerations both compromise on what's technically correct. However, they both do so in order to make a solution possible that's better and more useful than what we already have.

There's nothing technically wrong with using a G5 BC for a bullet that matches that standard better, as long as you have reliable data that indicates that the projectile actually does match that standard better AND you understand that you can't compare a G5 BC with a G7 BC.

My prescribed advice of using G7 BC's for long range bullets is a balance of many considerations including what's technically right, and what's a practical solution that the majority of shooters will be able to apply. A solution that's perfect in it's technical completeness will probably not get off the ground because it's overly complicated and has too many 'gotchas'.
The entire thread can be found here:
Applied Ballistics for LR shooting ??s

There's nothing wrong with using the most fitting standard in each case, and if a shooter is skillful enough to do it without getting them mixed up, has good enough data to support a match to one standard over the others, and understands that a BC referenced to a unique standard is not comparable to any other BC.

In my mind, referencing all long range bullets to the G7 standard exclusively is a solution that's easy to apply, removes most of the velocity variation of BC's, and maintains the ability to compare bullets by BC. It's not wrong to reference BC's to other (better) fitting standards, but in my opinion, that approach is too complicated for general consumption by the shooting public. The accuracy gained is just not worth the added complexity (again, this is arguable, and is only my opinion).

Thanks again for your valuable input.

-Bryan
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  #16  
Old 08-20-2009, 08:58 AM
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Re: Berger Bullets' Move To The G7 Standard BC By Bryan Litz

Hey Bryan,

My pleasure entirely, and again, I really do appreciate your work here. Your response here is something that I'd like to take advantage of to make things a bit clearer. You've stepped off the map of the known world here, in exposing a greater audience to the G7 profile. My concern here is, how many folks now think there is the G1 and G7 models, end of story? You've already done a sterling job of getting the ball rolling here, so let's not let it lose its momentum! What I'd like to see, on an open forum like this, is a brief explanation of the other models out there. Starting with Lowery's G series, specifically the lesser known G2, G3, G4, G5, G6 and GL models and what they're used for. My interest here is not in seeing them become used for trajectory calculations, but just exposing the shooting public to their existance. The fact that there are tables dealing with a variety of bullet forms, that sort of thing. I think that many folks following this thread are already being exposed to some ideas that were previously unknown to the vast majority of the shooting community, and that's a good thing. I know your space was limited in the first book, but have you considered doing anything with a bit more historical background, explaining the origins of such drag models? Probably a bit of a specialty item, I know, but it really is a fascinating history, and I think many people on these boards would be interested in such matters. The original Gavre commision, Krupp, Mayevski, Ingalls, Hodsock, the British 1929 tests, etc., all leading up to the E.D. Lowery's G series (incidentally, so titiled as an homage to the original Gavre commision).

Even with the prevelance of computers and ballistic programs today, I don't expect to see all these models being used, for the very reasons you've already cited here; too cumbersome, and the problems created in making bullet to bullet comparisons that would inevitably result. I agree with you completely about that, no argument at all. But it is an interesting history, and it makes the current models much more undestandable. Puts them in context, as it were. Anyway, as I've said, you've already gotten the ball rolling here, so the hard part is done. You have a ready and interested audience, so what do you think?

Incidentally, I missed you completely at Lodi. Didn't even know you were there until I saw you listed in the results. I'm sure I saw you and just didn't recognize you (mea culpa!) and I do sincerely apologize for that. Would have loved to have had dinner with you, so consider this a rain check for the next time. I'll be at the Spirit of America match in Raton at the end of the month, if you'll make that one. If so, I know some pretty decent places for dinner in Raton or Trinidad . . .

Thanks,
Kevin

Last edited by Kevin Thomas; 08-20-2009 at 02:11 PM.
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  #17  
Old 08-20-2009, 01:12 PM
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Re: Berger Bullets' Move To The G7 Standard BC By Bryan Litz

Brian, once again you have written a great informative article. Thanks for the information. Admittedly I do generally use Nosler bullets (sorry lol) but I will be checking into the G7 drag function as a means to make a more accurate drop chart.

For starters I simply used algebra to get an approximate G7 by using Berger's published BC's. After thinking I realized that this is kinda defeating the purpose of getting accurate out of the box drop charts Maybe I should switch to the berger's lol! I'm scared of that darn Secant ogive in my freebore galore rifle ;)
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  #18  
Old 11-10-2009, 01:00 PM
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Re: Berger Bullets' Move To The G7 Standard BC By Bryan Litz

I'm a little confused. The definition of the BC is: "The ability of the bullet to maintain velocity, in comparison to a standard projectile " according to the artcile.
What I don't understand is why would the value of G1 BC's of good LR-bullets be lower than 1.0? For example, take any good long range bullet with a BC at around 0.6 and above. Would that mean it's got the ability to maintain velocity better than the G1 projectile by 60% ?
So if the standard G1 bullet would be fired with 3000fps, and has lost 1000fps at a given distance, would that mean a G1-BC 0,6 bullet would have lost only 400fps at that same distance?

It's just... according to the definition I thougt a BC of 1,6 would do exactly that?
What if the "real" bullet is on par, or even worse at maintaining velocity than the G1 model?

Or is that mathematical comparison more complex than it sounds according to the definition?
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  #19  
Old 11-10-2009, 04:24 PM
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Re: Berger Bullets' Move To The G7 Standard BC By Bryan Litz

Check out this article
http://www.exteriorballistics.com/eb...oefficient.pdf

"The ballistic coefficient of a bullet is a scale factor (a number) which divides the standard drag to predict the actual drag on the real bullet."

I hope this helps,
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  #20  
Old 11-11-2009, 08:42 AM
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Re: Berger Bullets' Move To The G7 Standard BC By Bryan Litz

Thanks for the link! I think I understand what a BC really is now.
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  #21  
Old 01-30-2011, 08:47 PM
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Re: Berger Bullets' Move To The G7 Standard BC By Bryan Litz

Bryan
I have read your book several times gaing more insite everytime I read it> As you state in your book you need to know the drag coaficient in order to get the form factor to get the BC. You give all the formulas for everything else but for drag. It my rifle cannot shoot bergers then I want to use Nosler accubond 30 cal. 200 grain in my 300 win mag. Your book does not have the G7 BC for this only 180 grain . How or where can I get this BC. Do you Know this and can tell me? thanks
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