It's understandable why you believe this topic is "just hyperventilating" and you're right, none of this makes much difference at ranges out to 500 yards. Difficult as it may be to make first shot hits on targets at long range, a number of people are interested in doing so and they want the most accurate data available for bullets they might use. That's why Bryan is measuring and publishing G7 ballistic coefficients for many brands of VLD bullets.
It would have been useful to discuss this more with Bryan, but it looks like his comment was just a drive-by that mostly missed the mark as a result of his misconception that I was promoting G1 over G7.
His post did serve a usefully purpose in helping resolve a key issue.
I agree that the method described by Ken Oehler (deriving a G1 BC over long range based on tof) is the best way to derive a G1 BC, if you have to use a G1 BC. It's also the best way to derive a G7 BC.
That's has been one of my major points from the beginning of this topic. The means I used to demonstrate the merits of Ken's method relied on using published BC values rather than raw shooting data. I believe the limitations of using such data lead to most of the disagreements. As Bryan confirmed, BC's produced by Ken's method would be more accurate particularly if used to produce G7 BC values for VLD bullets.
That was stated in my third post where I wrote the following:
I speculate that a G1 BC produced by Ken Oehler's method would more accurately match the trajectory of Beger's #24530 then their published G7 BC over the velocity range most long range shooters use. If so, then I expect a G7 BC produced by Ken Oehler's method would be better still. Of course, shooters won't get better numbers if they think the current methods of producing them are the best. I applaud Beger for publishing G7 BCs, but feel there's still room for improvement.
I still feel there's room for improvement even if some manufactures are now using Doppler radar to calculate BC values. Regardless of the source of raw data, accuracy in calculating BCs comes down to the method that's used to process the raw shooting data. See the details in my response to Bryan.
In my first post I wrote the following:
The difference between G1 and G7 shows up in the transonic velocity range, which it seems few long range shooters use. Apart from magnitude, apparently the drag characteristics of supersonic flight are insensitive to bullet shape. Thus, you can't look at the shape of a bullet and tell which standard projectile it best matches in supersonic flight as it doesn't seem to matter much what the shape is. Maybe that explains why the industry seems reluctant to follow Beger in publishing both the G7 and the G1 ballistic coefficients.
This is confirmed by the following chart:
![[Linked Image]](http://farm4.static.flickr.com/3230/5840704020_8b6e35be14_z.jpg)
In the velocity range of Mach 2.6 to 1.7 (2900 to 1900 fps) there is no effective difference between G1 and G7.
Take any VLD or any other type of bullet's G1 BC and divide it by 2 to get the G7 BC. Plug the numbers into any accurate ballistics program and you'll find that for muzzle velocities up to 2900 fps and out to ranges where remaining velocity drops to 1900 fps there's no meaningful difference in predicted drop or velocity. For a G1 BC of 0. 502 and a G7 BC of 0.251 launched at 2900 fps JBM shows a drop difference of just 0.1 inch and a velocity difference of just 3.9 fps at 600 yards.
Beyond the velocity zone where G1 and G7 converge there's minimal difference between G1 and G7 from Mach 3 to Mach 1.2 (3350 to 1345) as can be seen in the following chart of larger scale (0 to Mach 4).
![[Linked Image]](http://farm6.static.flickr.com/5232/5854541038_8e8ba7a508_z.jpg)
This chart helps explain why G1 has been used so successful for so long. For the vast majority of shooters it doesn't make any difference if they use G1 or G7 BC values even with VLD bullets. Load the Berger #24530 to 3000 fps and fire it out to 500 yards and the difference in predicted drop is less than 0.4 inches (0.08 MOA) between the published G1 and published G7 ballistic coefficients. At that range the difference in predicted velocity is just 18 fps, which is within the variability of premium ammunition.
Some argued that the Mach 1.2 low velocity limit was my own invention despite having arrived at that number by consensus in another topic. In reality, Mach 1.2 is well known as the high limit of the transonic velocity zone as can be seen in the following quote from
Wikipedia External Ballistics.
The transonic problem: When the velocity of a rifle bullet fired at supersonic muzzle velocity approaches the speed of sound it enters the transonic region (about Mach 1.2�0.8). In the transonic region, the centre of pressure (CP) of most bullets shifts forward as the bullet decelerates. That CP shift affects the (dynamic) stability of the bullet. If the bullet is not well stabilized, it cannot remain pointing forward through the transonic region (the bullets starts to exhibit an unwanted precession or coning motion that, if not damped out, can eventually end in uncontrollable tumbling along the length axis). However, even if the bullet has sufficient stability (static and dynamic) to be able to fly through the transonic region and stays pointing forward, it is still affected. The erratic and sudden CP shift and (temporary) decrease of dynamic stability can cause significant dispersion (and hence significant accuracy decay), even if the bullet's flight becomes well behaved again when it enters the subsonic region. This makes accurately predicting the ballistic behavior of bullets in the transonic region very difficult. Further the ambient air density has a significant effect on dynamic stability during transonic transition. Though the ambient air density is a variable environmental factor, adverse transonic transition effects can be negated better by bullets traveling through less dense air, than when traveling through denser air. Because of this marksmen normally restrict themselves to engaging targets within the supersonic range of the bullet used.
Regardless of the reliability or accuracy of information on Wikipedia, the quote confirms Mach 1.2 was not something I contrived on my own to make the data support my argument. The reason most long range shooters stay above Mach 1.2 is also supported in another quote from Wikipedia.
Doppler radar measurement method: Some of the Lapua-provided drag coefficient data shows drastic increases in the measured drag around or below the Mach 1 flight velocity region. This behavior was observed for most of the measured small caliber bullets, and not so much for the larger caliber bullets. This implies some (mostly smaller caliber) rifle bullets exhibited coning and/or tumbling in the transonic/subsonic flight velocity regime. The information regarding unfavorable transonic/subsonic flight behavior for some of the tested projectiles is important. This is a limiting factor for extended range shooting use, because the effects of coning and tumbling are not easily predictable and potentially catastrophic for the best ballistic prediction models and software.
The useful range of a load is determined by where the remaining velocity drops to Mach 1.2. Those who want to go further should use larger caliber bullets if the Lapua Doppler radar data is to be believed.
Only long range shooters need G7 BCs and only for VLD bullets as most other bullet types fit G1 as well or better than G7. If you look at the number of viewers there are for this forum as compared to other hunting forums you soon realize that long range shooting is a niche market. Even within this forum many seemed drawn to this topic more by the colorful put-downs than the content.
Perhaps Large bullet manufactures don't want to confuse customers with notations like G7 that apply only to a minority of bullets, and Sierra handles the problem by publishing multiple G1 BC values. Maybe I'm wrong, but I don't expect the paradigm shift Bryan talks about will happen anytime soon outside the long range shooting niche.
