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AI - 308, twist rate? Right bullet

Baer45

Baer45
Full Member
Minuteman
Feb 5, 2010
147
46
69
Dublin, Va.
I have an older pre? AI in 308 it’s folding stock. It does not have the quick barrel change. I understand they come with a 1:10 twist barrel so I was thinking of 190gr SMKs...any thoughts?
 
I have an older pre? AI in 308 it’s folding stock. It does not have the quick barrel change. I understand they come with a 1:10 twist barrel so I was thinking of 190gr SMKs...any thoughts?

It will handle anything between 110 grains and 230 or so grains.

Barrel twist is one of the least important influences on accuracy.
 
I have an older pre? AI in 308 it’s folding stock. It does not have the quick barrel change. I understand they come with a 1:10 twist barrel so I was thinking of 190gr SMKs...any thoughts?
Not necessarily. The barrels with English proof marks are mostly 12 twist IIRC.
If your barrel is a marked AINA it is likely a Bartlein 5R and 10 twist. I have both.
While true that either twist may likely not affect accuracy at short distances it could very possibly have negative effects at longer ranges.
 
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If it is a factory barrel versus an AINA, then it is a 1:12 twist made by Lothar-Walther I believe. I shoot 168 SMKs if inside 600 yards and 175 SMKs for 600-1,000.

The 1:12 twist is not optimal for 175s but I have not experienced any issues
 
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I was reading Long Range Precision by Anthony Cirincione (vol 3) showing the Greenhill Formula and he decided to use a 1:11 inch twist to shoot 180 gr SMKs. So my thinking was a faster twist in 1:10 would jump up the bullet weight to maximize stability....I’ve always shot 175 gr regardless of twist but thought it might be fun to see the difference at1000.....
 
I was reading Long Range Precision by Anthony Cirincione (vol 3) showing the Greenhill Formula and he decided to use a 1:11 inch twist to shoot 180 gr SMKs. So my thinking was a faster twist in 1:10 would jump up the bullet weight to maximize stability....I’ve always shot 175 gr regardless of twist but thought it might be fun to see the difference at1000.....
I believe at some point the 11.25 twist was decided to be the "perfect twist" for 308. Sure do see a bunch of them on custom builds any way.
I shoot the 185 Hybrid ahead of Varget for a muzzle velocity of 2,780 FPS. The barrel is a 26" 10 twist Bartlein 5R chambered by Tooleyand screwed on my trusty AIAW. At the 1,000 yard mark JBM says it is still making 1,433 FPS using 50% humidity and 450 ASL altitude. It is stable and very accurate there. Were as a 20" it calculates to still be okay at that distance (even when adjusting the velocity down for barrel length difference).
My other AW currently has a 12 twist English barrel on it and I usually shoot 155 Scenar bullets thru it. Not because it won't stabilize others but I just like shooting those bullets.
I did try 168 SMK (which should be perfect for 12 twist) Federal Gold Medal Match at 1,000 yards in a AIAE MKII with 20" 12 twist once. The load shot one hole groups at 300 yards and well at 600 yards but it took quite a few rounds at the 1,000 yard target to determine those bullets were key holing at that distance.
 
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I love those Bartlein barrels! Not a suprise on the GMM 168’s...I will give those Hybrids a look! C