I've been looking into the "ideal" twist rate for a .308, and 1/10 seems to be the most popular.

however i found the perfect barrel for my build (profile, length, material, manufacturer, etc) and it is in 1/12 twist and 16"

from my understanding that will work fine with anything up to around 175g bullets

just wanted to check with the wiser minds around here before i start signing checks to start the build

1:12 is the twist for USGI M14 barrels and will stabilize 175gr bullets just fine.

Pick your bullet FIRST, then pick your twist rate accordingly.



ETA:  Try Berger's twist rate calculator http://www.bergerbullets.com/twist-rate-calculator/

...and personally I think you're better off with a 1:10 as it will stabilize a wider range of bullets from 155g to 200g.

Yeah if it were my choice i would go with the 1:10, but i need a specific barrel type (CHF, CL, rifle gas) and literally the only barrel i have found that works for that is 1/12 (hence this thread!)

1/12 will stabilize a 150gr cup and core projectile pretty well out to 700-800yds.

After 800yds even at 6600ft elevation, the gyroscopic stability I've seen from 1/12 comes apart like a random generator throwing shots all over the place with no predictability other than they will land somewhere out there.

If I was personally looking for a .308 twist with more reach, I would do at least a 1/9 twist from a 16".

If it's just a blaster for closer ranges, who cares.  Could even go 1/14" for 155gr or less.

At normal hunting ranges 400 yards and under the 1 in 12 will work for 180's and down, at least most 180's something like the 180 grain ttsx might be iffy especially in a 16" barrel(higher speed requires less spin)

well it turns out that hours of googling paid off and my barrel options have increased

so would the "perfect" twist rate for a 16" barrel be something like a 1/8 or 1/9?

I always like 168gr 308 regardless of the twist

Ive shot Berger 175s out of my 13 twist palma rifle and they shot fine at 1000 yards. Of course that was during the summer, and I had a 30 inch barrel.

B

thats almost double the length of my intended barrel lol

im thinking a 1/9 would be pretty spicy for the 16"

I am running 1/10 in both of my AR-10s and I regret EVERY DAY not going to 1/11 or 11.25.

I rezeroed my 1/12 Colt 901 today for FGMM at 100 yards. The 168gr SMKs pulled off 3/4" 5-shot groups multiple times shot from a lead sled. Including a couple 1/2" 3-shot groups in there. Seems pretty stable to me. YMMV.

Good luck finding an 8 twist AR-10 barrel off the shelf.

Columbia River, formerly blackhole, has a 1:8.5 option. I don't know if they have any on the shelf ready to ship, but it's not a custom job using a blank.

In the 80's I shot the National Match Course with a Winchester factory model 70 Palma rifle. It had a heavy 26" target barrel with 1:12" twist. I used 190 grain Sierra Match Kings for the 600 yard slow fire stage and it was very accurate.

For 190's, a 1:11" twist is probably closer to optimum (up to 220 grain). For 175 grain and less I would rather have 1:12". 1:10" is a hold over from the 30-40 Krag and should just be religated to the dust bin of history unless you're shooting 200 grain bullets subsonic through a suppressor.

If bullets were absolutely perfect, over stablelizing them would cause little harm - even 1:8". Since bullets aren't perfect, the faster you spin them past what is needed to stabilize them, the more your groups will open up.

1/8 works amazing in a 16" gun.

I've been shooting and spotting for 155gr, 167gr, 168gr, 173gr, 175gr, and 178gr from 24", 20", and 16" .308s out from 800-1100yds regularly for the past 21 years.

I definitely have seen 12 twist .308s come apart into unpredictable impact beaten zones past 800yds.

With 11.25" twist and 175gr SMK, I've made 1st-round hits at 1130yds in no wind conditions.

.308s are way too slow to "over-stabilize", especially with quality bullets like SMKs, AMAXs, ELD-Ms, Scenars, or VLDs.  Those companies spend a lot of time to ensure concentricity of the jackets, as well as uniformity of density in the cores.

If I wanted to beat my head against the wall some more with .308 Winchester, I would use a 1:9" twist in a shorter barrel because of the bullet I would pick, but I have zero interest in owning a .308 ever again for my uses.  I'm more familiar with it than any other cartridge for shooting distance just because of time behind a scope, and will give a good shooter very high hit probability wind calls with a 175gr SMK or 178gr Hornady, but I like 6.5mm much better for wind deflection, recoil, ability to track my own shot, and trajectory.

the heaviest i would be shooting is 175's

Armalite uses 11.25 in most of their barrels. They recommend 168 grain but I think 175 grain should work fine. My 16" carbine is pretty accurate with the 168's

Why? I find the 1/10 will stabilize a wide variety of bullets plus the heavies which have a higher BC then lighter weight bullets. I mainly shoot 178s and 190s in the ARs and the 1/10 works well at just above sea level, in the winter at 1k.

1 in 10 is probably the best overall twist.  It should shoot the 130's and 150's fine and will be better with the long 180's and up.  For a hunting rifle 1 in 12 works fine as it will work well with the short 180's like partitions and just about any 168's and down.  For hunting the 165/168's are really about the ideal weight in the 308, in fact you could just use a 150 grain ttsx for everything from deer to moose and be fine out to 350 to 400 yards.

Have 2 shorter (16, 19 inch) RR LAR-8's with 1:10 in barrels.  Neither one will shoot 150 and under bullets worth a crap, as compared to what they will do with 165 and 168 grainers.  My 16 inch M1A shoots 125-175 very accurately.  Believe it is over 1:11, but not sure.  Would prefer over a 1:11 inch for short barreled 308, didn't buy the shorter barrels for target competition.

I had a ruger 77 in a 1 in 10 that shoots anything pretty well.  Also have a savage 99 that I believe is a 1 in 10 that also shoots 150's through 180's well.  I just picked up a browning xbolt micro and it shoots 150 corelokts into one hole but also shoots remington 180's under a inch.    It didn't shoot the 150 gmx well but thats more than likely not a twist issue. maybe the semi's are more finicky, I don't know, all my 308's have been 20" inch or longer and bolts or levers. Honestly unless your shooting over 500 yards either twist should work with almost all factory ammo.

It may be the semi's, or just RR semi's.  They go from shooting well under moa, to 1.5 - 2 inch groups.  Don't have a bolt or lever less than 20 inch.  Would have to check what all the other 308's twists are.

I can't get light bullets to stabilize in EITHER of my 1/10 JP barrels.  Not for shit.  EXCEPT for 147 grain PMC Boat Tails....I have NO idea why that is...but it is very inconsistent.  Sometimes they shoot GREAT....other times...not so much.   The minute I hit 165 and above....both of my guns get into "the zonnnnnnnne".