"Truing" Ballistics Programs, Methods and Suggestions
I was curious on your personal procedures on truing your ballistics programs to fit your drop curves better. I'll share what I do and would like to hear if you have a different approach or suggestions how to improve.
I use Bullet Flight M by Knight Armament (no validation function like Xbal has), use Litz's G7 BC's, have a Kestral 3500 for atmospherics and a Bushnell 1500 ARC. I am satisfied with my ballistics output when it is +/- 3" of center at all ranges, I figure that for hunting three inches either way is negligible on a game animal.
After developing a load I chronograph it until I feel I have a very good idea of my MV. (Right now I shoot 210 Berger's at 2940 ES 8 fps for 22 shots out of my .300 Win. Mag. according to my chronograph) I then make sure my rifle is zeroed dead on at 200 yards. I then go out and shoot 5 shot groups on paper at 600, 800, 1000 and 1200 yards while entering all of the atmospherics data into the program from the Kestral (including Coriolis and spin drift) before each group. After the groups are fired I go home and locate the vertical center on all of the targets and measure the offset either high or low and then figure out the correct sight correction for every yardage. Then I go back and adjust MV and BC to match my results as best as possible. I don't like adjusting BC so if I can get away with adjusting the MV too much I much rather prefer that. After I think i've fixed it mathematically I go out and shoot it again to see. If I am off consistently a click or two after the second firing at ALL ranges, I will just drop my scope turret down a click or two and set the dial back to zero and call it good. This has worked well for me in the past and I have been successful out to 1,478 on steel using this method. From the MV given above I had to adjust MV from 2940 to 2970 without any scope or BC adjustment in order to have a curve that was on +/- 3" from center on all of my targets (800-1,200 yards). Or I could adjust the G7 BC form 0.323 to 0.340 without any MV or scope adjustment and still be on. I have however been using the adjusted MV in m program.
I'm curious on feed back as well as hearing your folks opinions/methods.
Re: "Truing" Ballistics Programs, Methods and Suggestions
Sounds OK but there could be a few variables that you need to consider that may make a difference. Below is a list that I have put together to remind myself that it is not always easy.
Best to repeat your testing a few times under ideal conditions if possible.
At the end of the day if you are hitting steel out to 1400 yards you are doing real well. Sounds like you are on the right path.
1. The Shooter.
2. Scope calibration error
3. Chronographed velocity wrong.
7. Atmospheric readings wrong.
9. Distance measurement error
10. Variations in rifle hold, rear bag placement, recoil control, cheek weld etc between different field shooting positions.
11. Change in velocity due to powder temp.
12. Failure to obtain precise zero.
13. Using G1 B.C.'s at extreme velocity and distance. (with boat tail pills.)
14. Errors in ballistic software.
15. Scope height error.
16. Click value of scope different to what manufacturer states.
Last but not least the B.C. value of the bullet!