338 300gr BC

canderson · #1 10-01-2010, 05:09 AM

Hey guys,
I am having a little difficulty in getting a ballistics program to match the drops I am getting with my 338 Allen. I have tested the velocity with two different chrongraphs (they both measure within 30 fps). The corrections with several different programs will be at least 1 MOA from what I actually have to use to hit the target. Any help is greatly appreciated as barrel life is very precious on this one. Thanks in advance.
Chris

jeffro · #2 10-01-2010, 10:03 AM

Have you checked your scope to see if the adjustments are tracking correctly.

canderson · #3 10-01-2010, 08:27 PM

Yes, it has been awhile. It is a nightforce and I believe the clicks were just a little over the 0.25 moa that is stated (0.258).

jeffro · #4 10-01-2010, 08:57 PM

What 300gr are you using, and what program.

trebark · #5 10-01-2010, 09:14 PM

I have found with most software that the 'ideal' trajectory rarely matches reality. I use exbal and it has a trajectory validation function that helps to move 'ideal' to 'reality'

jmden · #6 10-01-2010, 11:12 PM

Quote:

Originally Posted by trebark

I have found with most software that the 'ideal' trajectory rarely matches reality. I use exbal and it has a trajectory validation function that helps to move 'ideal' to 'reality'

yep...yep...doing this should get you squared away quickly regardless of what your chrono says. Don't get too hung up on what the chrono says...it's much more important, obviously, to hit what you're shooting at by matching the program to your actual trajectory. Might try using Bryan Litz's bc number (g1 or g7) for the 300g pill you're using. I'm shooting the 300SMK at 2980 and using his numbers for it, I haven't even had to do any trajectory validation, but I usually do with other loads/rifles. Good luck.

jwp475 · #7 10-02-2010, 09:54 AM

Quote:

Originally Posted by canderson

Hey guys,
I am having a little difficulty in getting a ballistics program to match the drops I am getting with my 338 Allen. I have tested the velocity with two different chrongraphs (they both measure within 30 fps). The corrections with several different programs will be at least 1 MOA from what I actually have to use to hit the target. Any help is greatly appreciated as barrel life is very precious on this one. Thanks in advance.
Chris

30 FPS off will cause a lot of problems. Use the trajectory validation feature on your ballistics program