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G1 vs. G7 profile... does it really matter???

Hello,
I know that the G7 profile bullet more closely matches the projectile I shoot but I have a Kestrel4500 with the Horus ballistic software. It is only available in G1. I had a piece of steel that was 20x40 in. at 1774 yds. and my Kestrel was on or either so close that I could not tell the difference. In a laboratory and controlled setting the difference could be more evident but in the real world does it really matter? If memory serves the military software is G1.

What do you think?
Thanks
 
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If G1 works for you in your shooting situation, OK.

The military in WW1 used G1 (then called G table; based on French naval artillery firings) because nothing else was avaiable. During the twenties, at Aberdeen extensive firings were done to obtain drag models G2 (originally J) through G6, and during WW2 the additional models G7 and G8 were introduced. G7 and G8 are based on British firings, by the way. The Army would not have done this if G1 were a good fit to modern projectile shapes.

The .30 ball M2 firing table, based on firings done in the twenties with the M1906 bullet, is computed based on G1, but with dozens of different BCs along the trajectory, starting with 0.410 at the muzzle and going down to 0.195 for very long ranges. If BC 0.41 had been used unchanged, a much too optimistic trajectory would have resulted.
In General Hatcher's Notebook firing tables using G2 are printed for .30 ball M1 and .276 Pedersen (both boattailed).
The military .30 AP M2 firing table of WW2 was calculated using the G5 drag model (also boattailed).
Today, the military uses individual drag curves for each projectile type, made available by the Firing Tables Branch (FTB).
 
In my experience, no it doesn't matter. I personally use Pejsa based G1 ballistics and get excellent solution predictions well beyond 1000 yards. I do confirm and calibrate my ballistics, but do that regardless if G1 or G7. Have had 1st round hits at 1-mile with in 1/2-MOA of POA.
Donovan
 
Thank you guys.
eternal student,
Go to the BALLISTICS CALCULATOR under the BALLISTICS tab on the BERGER BULLET website. Pick a boat tail bullet, (VLD,HYBRID, LRBT) and run it through the calculator using the G1 and then the G7 BC to see what the differences are. We always suggest you use the G7 BC with any Boat tail bullets and the G1 with the flat base bullets. gstaylorg hit the nail on the head . The G1 BC is based on a flat base bullet with a pointed nose and is "velocity banded" The SIERRA manual uses the G1 BC but they also include the velocity bands where it is most accurate. The G7 BC is based on a boat tail bullet and is good at any velocity . We only include the G1 BCs due to the fact that some ballistic programs like your HORUS only recognize the G1 BC and for use with our flat base bullets. Chapter 2 of Bryan Litz's APPLIED BALLISTICS for LONG RANGE SHOOTING goes into Ballistic Coefficient in a lot more detail. I suggest his series of books on Ballistics and Accuracy very highly.
Take care,
 
If your application is a contest with multiple sighters at a known and fixed range, using G1 will be fine.

G7 really shines when you need to hit a target with the first shot at a range you may never have fired that load before.

I also prefer G7 when comparing wind drift and retained energy. G1s (especially from the manufacturers) can give misleading results.
 
If G1 is working for you then nope doesn't matter.
If it is not. Then you can always blame external ballistic issues because its never the shooter. hahahahaha....
 
One significant point to make about comparing your bullets trajectory to that of the G1 or G7 drag model is that although it may be accurately predicting the point of impact at one distance, it is over the entire time of flight that the G7 will be the closest representative model. It would be very easy to say go to the range, shoot at 1000 yrds using the G1 drop, make adjustments in the field to get it perfect, go home and tweak either BC or MV in your solver to true its 1000 yrd predicted drop with your actual findings. If you then held up that chart with one that is using G7 they would give the same 1000 yrd prediction but may be 1 1/2 MOA high or low at say 400 yards. I've played with 2 ballistics programs side by side as an experiment, 1 using g1 and one using g7, and it is difficult to get them to be close at all ranges over a given trajectory no matter how you falsify the MV or BC. Just my observation but I am in no way an expert. Jesse
 

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