Can't get ballistic calculations to agree

[lisagrantb]

1:9 RH 27" long

 

[Mike6158]

I thought about something after I posted. You're getting decent accuracy... so it's not likely to be a stability issue.

That said, 1 in 9 is a little slow for 180 grain bullets according to some articles that I've read and others say it will work.

 

[Bart B]

The reason all the ballistic calculators, programs, spreadsheets and rules of thumb don't agree is simple.

There's different formulas, standards, approximations and other stuff for a given bullet. Everyone gets to choose which ones they use.

If you want good numbers, use programs that use ballistic coefficients obtained by actual firing tests at different velocities for each bullet. Some bullets may well have five different BC values; one for each of five velocity ranges. Don't use any program or calculator listing only one BC for a given bullet. The more BC vs speed values there are for a bullet, the more accurate the answer will be.

As far as angular measurements are concerned, there's four different world standards for a mil and two for minutes of angle. You need to know which one your number cruncher uses.

 

[Mike6158]

If you want good numbers, use programs that use ballistic coefficients obtained by actual firing tests at different velocities for each bullet.

That's one of the things that I like about the Trajectory Validation portion of the G7 Ballistics Calculator... but it doesn't allow for building a velocity / BC chart. Whose program does?

 

[lisagrantb]

I don't think it's a stability issue because during load development I was getting good groups with 300 fps slower. I have developed good dope for numerious other bullets using Bryan Jitz's BC's and had excellant results, I thought this would'nt be any different, maybe I'm wrong on this one. I use a mill meaning 3.6" @ 100 yards.

Thanks for the input guys.

 

[Loner]

I had no idea what dk was. It appears a software maker has invented a new term for
an old problem. It may be the answer to why your numbers are off. DK is used with a
g1 bc to correct it. Are you sure it will work with g7 or Litz bc numbers in your program.
Because it is not designed to.

http://longrangeshooter.com/2009/11...parison-nightforce-x-ball-lex-talus-delta-iv/

 

[lisagrantb]

I have used Bryan's G1 bc numbers to predict bullet flight profiles for 22, 6mm, 6.5mm, 257, 308 and 338 VLD type bullets with great success. I never even had to adjust the DK value off the default .5 value, that shows how accurate the BC numbers are from Bryan. This is the first time I've tried it with the hybrid Berger bullets, but in theory it shouldn't matter if the BC is accurate. the DK method developed in part by Arthur J. Pejsa is a highly accurate way of calculating trajectory.

 

[Loner]

I wasn't aware his numbers were based on g1. I thought they were on g7. But in either case they are different than g1 and shouldn't be re-corrected with dk.