6mmbr bullet choice

[Guesty]

Thank you very much for your detailed reply, that was just the info I was hoping to find.

I will go for a 1:8" barrel and 0.060" freebore as that appears to be the best compromise for me.

I have had a 6BR before for a short while, a Norman Clark converted Musgrave single shot target rifle. It had a Pac Nor 1:8" barrel that was great with 107gn Sierras but not so good with the 70gn bullets that were not long enough to get near the lands.

6BR has somewhat captured my imagination and I predict that I will have quite a few barrels over the coming years.

I have had a rethink and decided to go for a 1:10" twist instead as a I want to get the very best out of the 87gn Vmax and similar. I'm not too bothered about anything under 70gn.

I have read a report on 6mmBR.com that at least one 1:10" user has got the Berger 95gn VLD shooting well so maybe the shorter 95gn TMK might work also. With that in mind should I stick with a 0.060" freebore or go even shorter?

[Laurie]

I have had a rethink and decided to go for a 1:10" twist instead as a I want to get the very best out of the 87gn Vmax and similar. I'm not too bothered about anything under 70gn.

I have read a report on 6mmBR.com that at least one 1:10" user has got the Berger 95gn VLD shooting well so maybe the shorter 95gn TMK might work also. With that in mind should I stick with a 0.060" freebore or go even shorter?

 

 

A 1 in 10" twist won't 'get the very best out of the 87gn VMax' - far from it as the Sg at 3,000 fps is a calculated 1.28 under standard conditions when you're looking for 1.50. That's standard conditions too, so if you're after a fox on a cold sub-zero winter's night with high atmospheric pressure, it drops to around 1.16. In the latter conditions you need an 8.8" or faster twist to get full stabilisation.

 

The 95gn Berger VLD at 2,900 fps needs an 8.4 or faster twist under standard conditions, or the full 1 in 8" for the hypothetical cold winter's night to get the optimum 1.50 Sg stabilisation factor value, so the odds are that the TMK needs the same or potentially slightly more as the plastic tip increases bullet length compared to an equivalent shape HP design.

 

Beware of things you see in this field on Accurate Shooter - half these guys do their shooting at higher elevations than the top of Ben Nevis in 80-deg F + temperatures, often 90-deg +.

[onehole]

I have had a rethink and decided to go for a 1:10" twist instead as a I want to get the very best out of the 87gn Vmax and similar. I'm not too bothered about anything under 70gn.

I have read a report on 6mmBR.com that at least one 1:10" user has got the Berger 95gn VLD shooting well so maybe the shorter 95gn TMK might work also. With that in mind should I stick with a 0.060" freebore or go even shorter?

Stick with the 1:8 ,,,,believe me,,,,,the 87 Vmax will be just fine and the 95TMK very happy in 1:8,,,,,Laurie is spot on,,,,,,O

[Chris-NZ]

This över-stabilised" thing is way over-stated. You can definitely have too slow a twist but rarely issues going the other direction.

 

It's only if you're driving hyper-explosive bullets at hyper velocities out of a big case that you might get them coming apart in a fast twist. Rarely is accuracy an issue with "over spinning". The problem is more likely to be you have to jump them a long way because of the longer freebore you've chosen for your heavy bullets.

[Guesty]

Thanks all for the reality check.

I was worrying about over stabilising shorter Varmint bullets now I understand the science behind it all a little better.

Back to 1:8" then!