AR-10 308 Twist

[Phil3]

I am ordering a .308 barrel from Krieger for an AR-10 project. I intend to shoot at 100 yards, sometimes at 300, and rarely at 600. 800 would be the very outside, but not important...short - midrange accuracy is most important. Looking for best accuracy out of this gas gun, which will be shot off a bench. Was considering the Sierra Match King 168 grain. If this would be a good bullet, what twist rate? Krieger recommends a 1:12. I do not know if the AR-10 which bleeds off gas pressure to operate the bolt will slow velocity and perhaps warrant a different twist than a bolt action. Barrel length is expected to be 22", perhaps 24" at most. Many AR-10s use 1:11 or 1:11.25. I have also heard that spinning the bullet just enough, but not too much is advisable. ??? I just want to make the right selection on twist the first time.

Thanks.

- Phil

 

[Bob3700]

A 12 T bbl will stabilize a 175 SMK with no problems out to 800 yds.

I have owned both 10 and 12T bbls in 22" bbls and can't tell the difference in accuracy. For shorter ranges, you can shoot down to 125 gr bullets (I chose Speer TNTs) and they will surprise you with their accuracy.

The 155 SMK Palma bullet is also a winner in either twist.

Give those a try on top of Varget and you won't be disappointed.

Bob

 

[Laurie]

A 12 T bbl will stabilize a 175 SMK with no problems out to 800 yds. [Bob]

+ 1 on that. 1-12" is a good compromise that works very well with 155s, the various 168s and the 175gn SMK. It will also stabilise the 175 and 185gn Bergers and the 190gn SMK, but I imagine they're over-heavy for a gas-gun? (Not a problem here, as we're not allowed semi-autos except for .22 rimfires.)

spinning the bullet just enough, but not too much is advisable. ??? I just want to make the right selection on twist the first time.

That's only a real issue for the 100-300yd benchrest shooter looking to shave the last few hundredths of an inch off groups sizes, or those forced to use poor quality and badly balanced milspec bullets, as when we had to shoot 144gn - 146gn NATO 7.62mm ball ammunition here in 'Target Rifle'. Today's match bullets are very well made indeed and a theoretically slightly over-fast twist / rotational speed won't affect them, at least not so much you'd ever notice, especially when fired from a well made barrel like a Krieger.

My .308W Barnard F/TR rifle has a 1-10" twist Broughton tube to let me use 210gn VLDs at long range, but will still shoot quarter to half-MOA groups with the Berger 155.5gn BT FULLBORE Palma bullet.

Laurie,
York, England

 

[msalm]

I just built 3 AR10's and used 1-11.25" twist Rock 5R barrels. They shot very well with the 168gr A-Max loads I fired in them for testing.