Question about twist rate on barrels.

[I Am Hero]

Ok I need this answered once and for all because I hear different things every time on this: Does a faster or slower twist rate shoot heavier bullets?

First I had the understanding that a 1:7 AR shot the 45-52 gr really nice and that 1:9 shot 52-65 and so on. Now I was just reading someone's post who said that they shoot 69 gr or heavier out of their 1:7.

I figured there are probably forums about this out there on SH but when I searched "twist rate" a ton of articles come up.

 

[wnroscoe]

Re: Question about twist rate on barrels.

Yes, faster twist = heavier bullets

 

[Graham]

Re: Question about twist rate on barrels.

Yup: Twist rate is more a function of bullet bearing surface than weight, but that means that heavier bullets in the same caliber need a faster twist.

http://www.riflebarrels.com/articles/bullets_ballastics/bullet_imbalance_twist.htm

 

[slashsplat]

Re: Question about twist rate on barrels.

All correct. I have found my 1:9 ARs shoot up to 68/69 grain very weel, but nothing heavier. For that I go to 1:8, 1:7.7, or 1:7 to go up to 75 and 80 grain. I always match bullets to rifles starting with the HEAVIEST I have and working down to the best accuracy.

 

[targaflorio]

Re: Question about twist rate on barrels.

The idea is to stabilize the bullets correctly. Heavier bullets typically need to be spun faster to stabilize in flight. Berger usually lists the twist necessary to stabilize their bullets, even on the box.

The downside of fast twist is the possibility of adding pressure and decreasing muzzle velocity, and over spinning lighter bullets.