Best Twist rate for .308, what about 1-10

S

superking75

Inactive
I am looking into getting a .308 rifle and an wondering what is best.
The rifle I am currently looking at has a 1-10.
I plan to shoot 150 grain bullets.
 
My 10 twist F-T/R .308 does as well with 155 Scenars as it does with the 175 SMKs I specified the 10 twist for.

Don't overthink it, shoot.
 
1:10" twist is the factory compromise to shoot everything up to and including 220 gr bullets. You can go with that or try a 1:11" twist for lighter bullets.
 
When the U.S. Army adopted the .30 caliber around 1891, they did a lot of expensive testing and decided on the 1::10 twist. If it has been good for 125 years it probably is OK.

Jim
 
Winchester's original twist for the 308 (And the M-14 rifle) was 1-12"
1-10" is ok too. Many 308s today are twisted 1-10"
If you are only going to shoot bullets up to 180 grains the 1-12" is fine and the slower twist drops the pressure a tad and also increases the bore life a tad.
"Tad" being so small an amount as to not really matter. But there is no "down side" to the 1-12" for most applications.
 
If you look at Palma match rifles in .308 for those 155's they all seem to have 13" or 13½" or 14" twists. Some folks shooting light varmint bullets in this diameter get 16-18" twists.

The 10" twist was developed for the 220 grain RN FMJ issued in the 30-40 Krag, and they experimented with some heavier ones, but probably didn't like the recoil. Anyway, for those big bullets 10" was probably a near optimal choice. Lighter bullets don't need to spin that fast. They just didn't bother to change it for 150 grain bullets when they went to 30-06, even though a 12" would have been plenty, even in pretty extreme cold weather. Then they came up with the 173 grain bullet, and the 10" shot that happily, too. Today, the 5R rifling in the M24 is geared to the 175 grain Sierra MatchKing bullets, which are just slightly shorter than the 173's, owing to a shorter boat tail, and its got 11¼ inch twist.

At the same time, match bullets are so well made these days that it seldom seems to hurt much to have a faster twist. Any mass asymmetry causes a bullet to spin eccentrically, and the faster it spins, the more eccentric the spin around the trajectory line is (aka, wobble). This causes groups to open up. Back when the 10" twist was devised for the long, heavy bullets, it was probably the minimum that met military requirements under all expected weather conditions, as extra spin decreased accuracy. Today, benchrest shooters firing shorter ranges use relatively short, stubby bullets so they can get away with slower twists. That's because, when you are shooting one-holers, you can still pick up on the spread caused by wobble due to over-spinning. But for those of us shooting half moa and larger, match bullets are made so well now that it is hard to see the error the extra spin causes, if you can see it at all.

Other effects from spinning more than necessary are greater spin drift and the amount by which the bullet rises or falls while deflecting left or right under the influence of wind, also increases with rate of spin.
 
Palma match rifles are also great, big, single shot, things.
1 in 10 will do. It's about the manufacturers mass producing .30 cal barrels and chambering it in whatever cartridge they need. Let's 'em use the same barrel blank for a .308, .30-06 and all the rest of 'em.
 
Unlike 30-06 rifle makers can't seem to make up their minds on 308. Almost all 30-06 rifles are 10 twist and I think that should be standard for 308. But you see many 11 and 12 twist 308 rifles. I own 3 and have 10,11, and 12 twist barrels. All have been just fine for me with 150-180 gr bullets. I'd guess the 11, and 12 twist would theoretically be at a disadvantage with anything over 180 gr.
 
You must log in or register to reply here.
Back
Top