Very Short bearing surface bullets...

[mike mccormick]

Are you using the Sierra 2231s? If so, they like .040- .045 jump in my rifle. Running 2681 fps .BTW....9 twist is fine with these bullets. Mine is shooting 1/4 moa @300yds

 

[Ned Ludd]

6BRinNZ - Perhaps I missed it, but I didn't see exactly what bullet you are using. If you don't want to mention it in a public forum, PM me, we may be using the same one, as I have recently been using a very long 200 gr .308 bullet in a 9-tw barrel that exhibits the exact same behavior you're describing. Nothing I have tried seems to work and I have tried quite a few different things that ordinarily should have solved the issue. Berger's [shorter] 200-20X bullet shoots fine from the same barrel, so I don't believe the twist rate is the problem. Other have mentioned to me that they had the exact same problems with this bullet. I'm beginning to suspect there's more to the poor grouping than just the short bearing surface. I have loaded bullets in the past with relatively short bearing surfaces without issue. It is possible that some other design features such as the location of the Cg may be coming into play. Occasional groups will be fine, but the [bad] flyers occur at a frequency that is high enough I won't use this bullet in competition at this point.

 

[6BRinNZ]

Are you using the Sierra 2231s? If so, they like .040- .045 jump in my rifle. Running 2681 fps .BTW....9 twist is fine with these bullets. Mine is shooting 1/4 moa @300yds

Mike you lucky bugger - that sounds perfect! No I'm not using the Sierras. They came in more expensive than Berger Hybrids!
What FB did you go with on your reamer? I went for .105 and think that is too long now.

@Ned Ludd - I'll send you a PM. I haven't listed the bullet as I didn't want to come across as bagging it.
You are the second person that's mentioned using a 9tw on other shorter 200s and they are working well so while I think twist plays a part in precision (SR BR proved this a while ago I guess) I don't think it is the major player relative to the groups we are seeing.

 

[mike mccormick]

Mike you lucky bugger - that sounds perfect! No I'm not using the Sierras. They came in more expensive than Berger Hybrids!
What FB did you go with on your reamer? I went for .105 and think that is too long now.

@Ned Ludd - I'll send you a PM. I haven't listed the bullet as I didn't want to come across as bagging it.
You are the second person that's mentioned using a 9tw on other shorter 200s and they are working well so while I think twist plays a part in precision (SR BR proved this a while ago I guess) I don't think it is the major player relative to the groups we are seeing.

My barrel is a Bartlien gain twist. 9.5-9
Frank at Bartlien chambered it with a SAAMI 308 reamer, and it has tons of freebore. I only have about 0.125" bearing surface in the case neck. Using 0.0015" neck tension and 45.8 gr Varget. Starline Match small primer brass. My ES is 5. SD of 1.3

 

[6BRinNZ]

Its official I am giving up on these bullets. .007" jam showed promise but no amount of tweaking depth, powder, neck tension or tuner settings would help bring in the group size or consistency.
I've tried different powder charges large jump small jump, jam, neck tension, tuner settings on and on and always the same...promise and then the next group or two on, it would blow out to nearly 1.5 moa at 100 yards.
I've learnt heaps but I'll park these.

Thanks to all for the suggestions and a happy new year and best wishes to you all.