Barrel twist rate, velocity and bullet weight

[lonestar2222010]

I'm curious with a fast twist rate of 1:10 in a 22" barrel would a heavier grain bullet (180gr .308) be more accurate with a faster or slower velocity?
Same for a lighter bullet (150gr) In the same barrel.

 

[rcmodel]

The higher the velocity, the less twist a long bullet HAS to have to get enough RPM to stabilize it.

But, the 'standard' twist for a .308 is 1/12".

SO, a 1/10" should stabilize anything you can put in it.

1/10" worked for a century in 30-40 Krag and 30-06 with 220 grain RN bullets.
And all lighter pointed ones.

Lighter bullets doesn't matter.
You can't really over-stabilize a bullet, until the jacket comes apart from centrifugal force and the bullet turns into a grey streak of lead smoke just down range.

rc

 

[Thompsoncustom]

I think the 308w is good up to 250gr or at least that's the highest any of my manuals go. I reload 230gr in my 16in 1/10 ar-10 and they stabilize fine even at slower speeds.

Here's a calculator for ya

http://www.bergerbullets.com/twist-rate-calculator/

 

[spitballer]

Increasing velocity to introduce stability has always seemed somewhat disingenuous to me although I understand the theory. I find the gains to be small and not worth designing a barrel around, especially if a slightly faster twist will give a broader, more versatile velocity range for a given projectile.

Nevertheless, increasing the velocity is an option that can make the critical difference for a marginally stable projectile, for sure.

 

[moxie]

"..grey streak of lead smoke.."

RC, you're terrific!

 

[Jim Watson]

As spitballer says, bullet stability is not very dependent on velocity, one article said only by the fourth root. Increase velocity 10%, you only increase stability 2.4%. And 10% is a BIG increase in velocity.

Get the right barrel to start with. But don't agonize over it, nobody worried about rifling twist until the Army bought .22s.