G1... G7... ??

Kevin,

I meant no disrespect to Sierra or any other bullet manufacture. I talked to Sierra and Nosler and couple other bullet manufactures back in the late 90's about readdressing the G1 BC issue and was politely told no thanks but thanks for the suggestion. Now, I do not remember who I spoke with back then but I made the attempt explained my reasoning.

You've brought up a lot of valid points about past and present theories and technologies. With that said, Sierra and the other bullet manufactures have the ability, access to new technologies to make the necessary changes shooters are and have been asking for. I understand they can't do this over night, but conveying information to the shooting community that they are in process of changes would be very helpful.

However to remain in a status quo mode in my mind is somewhat turning their backs on shooting community.

If I offend you or your friends you have my apologies as I meant no disrespect, I was simply stating the short comings of using the G1 drag model and why it's not the model that should be used today. It may have worked in the past…to a degree and was as you stated what was available at the time. Nowadays there are much better and more accurate tools.

Hope it helps,
 
Jeff, no worries, I didn't take it that way at all. I just wanted to provide a little insight into what goes on behind the scenes of the industry. You're absolutely right that things are changing, and pretty damned quickly these days. Part of the blessing (and curse) of the technologies I'd mentioned earlier.

That said, I'll tell you flat out, there's significant portions of this industry that are firmly stuck in the mud. That was the inertia I alluded to. I don't see much of that changing anythime soon, and a couple that have dug their heels in all the more deeply, determined to resist any such new-fangled ideas from intruding on the "we've always done it this way" mentality. Yeah, there's a lot more of that attitude around than most would care to admit. On the up side, there's some hope out there too. Lapua, for example, is doing a tremendous amount of their exterior data based on actual doppler radar firings. With the tie into Nammo and govt. ammunition contracts, that's a major asset that trickles down to the individual shooter. Sierra used to do some radar firings when they could get access to Yuma Proving Grounds, but the contact that got that in was lost some years back. Don't see that happening again anytime soon. The process is time consuming, and requires some phenomenally expensive equipment that is well beyond the means of even the most successful commercial bullet makers. As far as most of our other domestic bullet makers, you'd have to ask, but I'm betting you'll hear a lot of, "G1 'cause that's the way we've always done it" explanations.

If most of these get dragged into using the more modern (or at least, more suitable) drag models, it'll likely be kicking and screaming all the way.

Don't sweat it, there was no offense taken, and certainly none intended. Just thought it was worth mentioning, and migth be of interest to the readers.

Sincerely,

Kevin Thomas
Lapua USA
 
Good reading...well now that i've read it for the zillionth time. Is it just me or do you guys find yourself having to read some of the science behind aerodynamic modeling etc etc several times before you can get it in your mind to where it starts to come together? Maybe it's just me.
 
Arthur Schopenhauer said:
"All truth passes thru 3 stages. First, it is ridiculed. Second, it is violently opposed. Third, it's accepted as being self evident."

I think we're somewhere between step one and two with properly referencing BC's. :)

There are those 'advanced users' who are tuned in and get it, but we all agree it will take a long time before the practice is common from the top down.

We did some BC testing at the Ben Avery range in Phoenix last week at 1000 yards. Mid Tompkins has a chronograph with 4' hardware (not optical) screens that can be hit and measure velocity at long range. Just for kicks, I brought along my acoustic sensors which measure time of flight. It was interesting to see how the BC's derived from the velocity data compared to the BC's derived from the TOF data.

Eric and Michelle did the shooting, I monitored the acoustics and MV, and Mid ran the pits and handled the downrange chrono. It was quite a party :D

Here are some interesting conclusions/results from the testing:

1) The G7 BC's derived from the velocity data were very similar to the G7 BC's derived from the TOF data. However, the G1 BC's were vastly different when derived from velocity as compared to TOF. The practical consequence of this fact is that if you're out to 'measure' the G1 BC of your long range bullet, you can arrive at a different number depending on how you measure it (velocity drop or tof). But if you reference the BC to a more appropriate standard, it doesn't matter what metric you measure, you will get a 'true' value that applies for all performance metrics.

2) The bullets that were shaped more like the G7 standard projectile (VLD's, .308 155 grain Lapua Scenar, .308 155 grain HBC (Australian made)) had the least difference in their G7 BC's, and maximum difference in their G1 BC's when derived from the different methods. Other bullets that have tangent ogives still matched better for G7 than G1, but a different model would be required to make a better match.
As an example, the Lapua 155 Scenar showed a G7 BC of .233 derived from the velocity data, and a G7 BC of .234 based on the MV and TOF. The difference is only 0.4%. The G1 BC was .453 based on the velocity data and .465 based on the MV and TOF data, a difference of 2.6% which is 'significant' in terms of predicted drop at long range. The Berger 155.5 FULLBORE bullet (a tangent ogive design) showed 2.2% difference for G7, and 4.8% difference for G1. I would bet that referencing the BC to the G5 standard would result in less than 2.2% difference because this bullet more closely resembles G5.
The point is that if you don't use the right standard drag model, you can arrive at drastically different results for BC based on how you measure it.

3) I was pleased to see that 8 out of 17 of the bullets tested matched my previously measured G7 BC's within 1%. All but 3 of the 17 matched within 2%. Achieving this kind of agreement despite the fact that we tested different lots of bullets from different rifles and different average flight velocities was very encouraging.

Regardless of how 'dug in' some of the others in the industry may be, the fact is that we're at the point in the shooting sports where shooters recognize the importance of good information. They're going to get it one way or another, it's just a question of how much trouble it's going to be. Lapua stepped up by providing the radar measured drag curves unique for each bullet which is golden information, but is not a practical option for most companies due to cost. Berger publishes G7 BC's. Sierra gives multiple G1's. All the others aren't yet offering anything but the G1 referenced BCs. Of course my book has G7 BC's for many LR bullets but face it, only a small fraction of shooters will know about and use that data compared to those who look to the bullet companies for BC's.

Jeff makes a good point about considering other standards in addition to G7. That point has been illustrated by much of my testing which shows an imperfect match of drag data to the G7 model, especially for tangent ogive bullets. There are a couple reasons why I continue to advocate the exclusive use of G7 referenced BC's including:

1) By using one standard for the LR 'class' of bullets, you maintain the ability to compare bullets by BC. If you don't use the same reference, you can't compare. For example, what's better, a G5 BC of .354, or a G7 BC of .345? I feel that the small practical difference in 'match' between BC's referenced to G5 vs G7 is not worth sacrificing the ability to compare bullets based on a BC that are all referenced to a common standard.

2) It's very difficult to measure with certainty which model a bullet matches best. It's clear that all long range bullets match G7 better than G1, but when you talk about G7 vs G5, the difference is more subtle. You might be able to do this with certainty after carefully testing the same bullet many times, but it's not a practical thing to consider applying to many bullets. I typically use 4 acoustic sensors spaced in 200 yard intervals from the muzzle to 600 yards and most of my data isn't good enough to distinguish between a G7 or G5 match with certainty. The biggest difference in the shapes of the standard drag models is near the transonic speeds where the flight quality of the bullets becomes questionable and 'rifle dependant' because of stability considerations.

If you're an advanced user like Jeff and do the testing to demonstrate that one drag model is decidedly better than another for a particular bullet, then you are correct to use that standard. However, because of the considerations raised above, I am of the opinion that opening the shooting world up to all the different standards as a common practice is not the right thing to do. Can you imagine a different standard drag model for each bullet type being invented? You would have the Accubond drag model, the SMK drag model, the Berger VLD drag model, the Tripple Shock drag model, the Grand Slam drag model, the Scenar drag model, the Vmax and Amax drag model, etc etc. And even then, they would still be a compromise for some of the bullets in their own line! The 178 AMax has a different ogive and boat tail than the 208 AMax. The 210 SMK is quite a bit different in shape than the 220 SMK. I truly believe that there is a lot of value in simplicity and limiting the scope of standard drag models to G7 for the LR class of bullets is the right thing to do for the general public.

Everyone stay warm and enjoy the holidays.

-Bryan
 
Hey Bryan,

As you might imagine, I'm sitting here with a large, Cheshire Cat style grin on my face with all these postings. This is exactly the sort of discussion that I've wanted to see on this topic. Thanks for all your contributions, they've been invaluable.

In the meantime, if you get back out for anymore testing, tell Mid and Eric I said hello, and give Miche a big hug for me.

Kevin Thomas
Lapua USA
 
Hey Bryan,

As you might imagine, I'm sitting here with a large, Cheshire Cat style grin on my face with all these postings. This is exactly the sort of discussion that I've wanted to see on this topic. Thanks for all your contributions, they've been invaluable.

In the meantime, if you get back out for anymore testing, tell Mid and Eric I said hello, and give Miche a big hug for me.

Kevin Thomas
Lapua USA

Mike,
We refer to that Cheshire cat grin as something else here in Texas, more like a $*it eating grin! LOL This was a great thread with lots of good and informative information.

Bryan,
I wish I had a job like yours where I could shoot and test for a living. I spent last night running and playing with numbers (the scream you hear in the back ground was my wife saying "give it rest already"!). Keeping with the G7 coefficient drag model provides the best all round solution for most types of boat tail bullet. Those that don't really fit nicely into the G7 model would still calculate better than using the G1 drag model.

I did state in my previous post that we'd be splitting hairs by using the G5 or G7 for most boat tails. By changing some of my known G5 BC's to G7 and re-running numbers didn't produce any significant changes in output data. Actually the changes were so small, they would have fallen into the human error category at distances of 700 yards or more.

So for the sake of argument and my sanity I'll fall in to the ranks and just say use the G7 coefficient drag model for boat tail bullets.

Mike and Bryan, great information and have a great holiday season...Merry Christmas everyone!
 
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