Home Forums Hunting & Shooting Ask The Gunwriters Twist rate vs. pressure?

Was talking to a guy the other day in Sportsmans Warehouse who was relating his results with his new 6.5-06. I have a 6.5-284 and have been giving him tips from my load development. In the course of our conversation he mentioned a buddy of his told him that a slower twist (i.e 1-10") was better to help reduce pressure so he could use a faster powder (he hasn't been getting the speeds he hoped). I just nodded politely and told him I had read that was part of the theory behind 'gain twist' barrels--to help 'ease' the bullet up to its rotational velocity. I also stated I had my 6.5 built with a 1-8" for shooting the 140s (and I was getting 3000 fps w/ the 140).

I understand the 'theory' of his buddy's statement but has anyone done scientific measurements of said theory? Do gain twist and/or slower twist barrels make a significant difference (pressure wise) all else being equal? I suspect not enough to notice and certainly not enough to justify a slower twist in something like a 6.5 where you would want stabilization for a 140 grainer.

Anyway, satisfy my curiosity if you would.

that's exactly how the 6.8spc 2 chamber came about. they altered the throat/ leade slightly and went to a slower twist to ease pressure. they found that they needed both the slower twist and throat mods to make it a complete package for lowering pressure......or so I've been told by RKIs.

advntrjnky

ETA: try pushing your car on a flat driveway with the wheels straight, turned slightly, and finally turned to full lock and see which is easier.

Interesting.

I've always wondered whether 308 Win's with a 1-12" twist (all else equal) are "faster" than the 1-10" twist... or does a 1-12" just require a bit more powder to match the velocity of the 1-10"?

I've no doubt there is a difference but wonder just how great it is. As Brad asked, is it enough to make a 1-12 .308 (for example) statistically on average faster than a 1-10 and by how much? I'm thinking it wouldn't be enough to notice past each barrels indivuality. BUT, I don't know--that's why i'm asking.

for most people i don't think it would ever make a difference, but for those guys who run right on the edge it does. for example: 1000yd palma guys trying to get the most velocity out of the .308 and 28" barrels or a cartridge like the 6.8spc that you need to get max performance out of tightly constrained parameters like in an ar15. For most people if you need more power/ velocity in a .308 sized action you can just go up to a .300RCM or .300WSM.

advntrjnky

None of that really is the point of the question...

Twist rate influence on pressure is probably too minimal to step outside statistical background clutter and it is probably impossible to prove overall advantage one way or the other. It takes precious little energy to spin up a bullet.

Spot on. I have seen pressure test in the 223 with the same ammo from 7 twist to 14 twist and the difference in pressure is meaningless