Need Help!

[WDH]

Let me first say hello!

I am having an issue with my groups opening up at 500yds. My gun is a custom 6.5x284. Kriger 27" barrel, Deviant action, McMillan stock and Nightforce glass. I used OCW test for load development and have a load that shoots in the .1s and .2s consistently (48gr H-4350 @2927fps berger 140 VLD set .030 off). At 500yds it blows up to 3.5+" All my other guns that produce good groups at 100 or 200yds continue to hold the same MOA out to 1000yds. Suggestions?

 

[DocDoc]

What is the twist?
Is it uniform or just vertical stringing at distance. If it is vertical, extreme spread in velocity can be the cause.

 

[WDH]

It is a 1-8 twist and the stringing is more uniform than vertical. The ES is around 12

 

[barefooter56]

It is a 1-8 twist and the stringing is more uniform than vertical. The ES is around 12

WDH,
"Stringing is more uniform than vertical". So is more horizontal or ? Pictures will help. At 3.5" at 500 yards you are still below 1 MOA in group size and with a ES of 12 your SD ( which is more important as it is an indicator of vertical dispersion should be less than that. Is this a one time thing or what? We all have our good days and bad days at the range.

 

[dok7mm]

I have had better accuracy with 8.5 twist and 140 VLDs, but I doubt that is your problem. More likely, it's something small like a seating depth issue or a variance in velocity. I use H-4831 and SD runs <5 fps. As rifles differ, it seems that as range increases, tweaking the small things makes a big difference. An unseen wind can open a group that much on a 140 or a slight neck tension difference. Hope you figure it out.