Is 1:8 twist too fast for .308?

[Merlin_019]

I am having a new AAC Blackout 18" 1:8 barrel mounted on my 700 in .308. AAC says 1:8 is the best all around for subsonic and standard loads. The little I've been able to find says that a heavier bullet will perform better. Someone else reports 1.5" groups at 100 yards with 168gr. Can anyone offer any good insight? Just loaded up up on 300rds of 168gr and I hope it wasn't a mistake!

 

[Alaskaman11]

Re: Is 1:8 twist too fast for .308?

There is Never too fast!

 

[Longshot38]

Re: Is 1:8 twist too fast for .308?

It is next to impossible to overspin a bullet. You 8 twist barrel should work just fine. At 100 yards you will not see the effects of that twist rate. However farther down range you will likely see more spin drift.

 

[Alaskaman11]

Re: Is 1:8 twist too fast for .308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Longshot38</div><div class="ubbcode-body">It is next to impossible to overspin a bullet. You 8 twist barrel should work just fine. At 100 yards you will not see the effects of that twist rate. However farther down range you will likely see more spin drift. </div></div>

Hey long, go ask Frank his views on Spin Drift. Don't worry about it, just go shoot the rifle! Have fun!

 

[bribri]

Re: Is 1:8 twist too fast for .308?

I have a 16 inch 308 with a 1 in 8 twist. So far 155 scenars are producing the best accuracy, under moa out to 600 yards.

http://www.snipershide.com/forum/ubbthre...389#Post2548389

 

[madd0c]

Re: Is 1:8 twist too fast for .308?

I don't know if t was my post you were referencing, but I also got about 1.5" groups with 168gr FGGM factory ammo from a 16" 1-8 AAC barrel.

I haven't done a proper load workup for the rifle other than for subsonic which was what i built it for, but when I get some time I plan on working up with 168, 175, 200 and possibly 240s for normal loads and not subsonic.

Your 1-8 can stabilize a 240, so might as well try some heavier bullets to see what they do.

If you work up a load specifically for the rifle, I am sure you can find a node with the 168s.

madd0c

 

[Qld4390]

Re: Is 1:8 twist too fast for .308?

Nope, 1 in 8 is not too fast for shooting standard loaded ammo. I run a 1/8 Pac Nor barrel and shoot 168 Fed GMM with no problems. Gun will shoot better than me, and is certainly not a 1.5 MOA gun due to the barrel.

 

[Graham]

Re: Is 1:8 twist too fast for .308?

It should be perfect for those 300gr subsonics! LOL!

Seriously, don't worry about it....yet.

 

[rcw3]

Re: Is 1:8 twist too fast for .308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Alaskaman 11</div><div class="ubbcode-body">There is Never too fast! </div></div>

Uhhh - I would not go so far as to say "never" as I have experienced issues with very fast twist barrels (for the caliber bore involved) where they can exhibit a great deal of pressure with certain bullets and loads even when the loads are moderate loads. An 8" twist on a 30 cal barrel is right there "on the edge" if not over sometimes - maybe fine - maybe it will exhibit some issues. For a .224" bore a 6.5 twist barrel is near the point of no return, and for a 6mm a 7" twist is typically over the top (stay with 7.5" as the tightest twist if you can), for a 6.5 mm, an 8" twist works fine but I would be wary of going any tighter, for a 7mm, an 8.5 twist is safe, but an 8" twist 7mm is "on the edge", and for a 30 cal, in my opinion, and 8" twist is flaunting it.

There's a point where the barrel twist rate becomes more like a wall and less like a ramp (especially with a bigger diameter bullet where it takes more force to take it from zero rpm to it's full rpm in fractions of a second). Subsonic loads can typically handle a faster twist but be wary of running full charge high velocity loads out of an "on the edge" twist, or you may be in for a surprise (super high pressures, blown primer, etc.).

I like staying in the safe zone myself. "Been there, done that" with some very fast twist barrels and unexpected consequences are not my idea of fun when I have 50,000 psi (+/-) going on right next to my face when I shoot a rifle.

 

[scotharr]

Re: Is 1:8 twist too fast for .308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rcw3</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Alaskaman 11</div><div class="ubbcode-body">There is Never too fast! </div></div>

Uhhh - I would not go so far as to say "never" as I have experienced issues with very fast twist barrels (for the caliber bore involved) where they can exhibit a great deal of pressure with certain bullets and loads even when the loads are moderate loads. An 8" twist on a 30 cal barrel is right there "on the edge" if not over sometimes - maybe fine - maybe it will exhibit some issues. For a .224" bore a 6.5 twist barrel is near the point of no return, and for a 6mm a 7" twist is typically over the top (stay with 7.5" as the tightest twist if you can), for a 6.5 mm, an 8" twist works fine but I would be wary of going any tighter, for a 7mm, an 8.5 twist is safe, but an 8" twist 7mm is "on the edge", and for a 30 cal, in my opinion, and 8" twist is flaunting it.

There's a point where the barrel twist rate becomes more like a wall and less like a ramp (especially with a bigger diameter bullet where it takes more force to take it from zero rpm to it's full rpm in fractions of a second). Subsonic loads can typically handle a faster twist but be wary of running full charge high velocity loads out of an "on the edge" twist, or you may be in for a surprise (super high pressures, blown primer, etc.).

I like staying in the safe zone myself. "Been there, done that" with some very fast twist barrels and unexpected consequences are not my idea of fun when I have 50,000 psi (+/-) going on right next to my face when I shoot a rifle.
</div></div>
rcw3....a bonafide expert. Don't know anything about sub-sonic loads, but 1:10 is the fastest I see anyone using for supersonic 308s.

 

[6XC]

Re: Is 1:8 twist too fast for .308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scooter-PIE</div><div class="ubbcode-body">
Don't know anything about sub-sonic loads, but 1:10 is the fastest I see anyone using for supersonic 308s. </div></div>

DTA SRS Covert has a 1:8" twist.
http://www.deserttacticalarms.com/guns/precision-rifles/dta-srs-covert-rifle-chassis-138.html
And I have seen a couple of other suppressed rifles that have had the same twist.

 

[rcw3]

Re: Is 1:8 twist too fast for .308?

I have shot with shooters using a 1:9" twist with the big 30 cal bullets with supersonic loadings.

In reality, I don't know of commercial ammo makers loading over 200 gr factory ammo for the 308 Winchester that's not subsonic, so I suspect the rifle makers are banking on the user of the 1:8" twist barrels running bullets that are 40 + grains lighter than the twist would enable the barrel to run when a supersonic load is employed and that may run o.k. in that setting.

 

[nmcclure]

Re: Is 1:8 twist too fast for .308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rcw3</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Alaskaman 11</div><div class="ubbcode-body">There is Never too fast! </div></div>

Uhhh - I would not go so far as to say "never" as I have experienced issues with very fast twist barrels (for the caliber bore involved) where they can exhibit a great deal of pressure with certain bullets and loads even when the loads are moderate loads. An 8" twist on a 30 cal barrel is right there "on the edge" if not over sometimes - maybe fine - maybe it will exhibit some issues. For a .224" bore a 6.5 twist barrel is near the point of no return, and for a 6mm a 7" twist is typically over the top (stay with 7.5" as the tightest twist if you can), for a 6.5 mm, an 8" twist works fine but I would be wary of going any tighter, for a 7mm, an 8.5 twist is safe, but an 8" twist 7mm is "on the edge", and for a 30 cal, in my opinion, and 8" twist is flaunting it.

There's a point where the barrel twist rate becomes more like a wall and less like a ramp (especially with a bigger diameter bullet where it takes more force to take it from zero rpm to it's full rpm in fractions of a second). Subsonic loads can typically handle a faster twist but be wary of running full charge high velocity loads out of an "on the edge" twist, or you may be in for a surprise (super high pressures, blown primer, etc.).

I like staying in the safe zone myself. "Been there, done that" with some very fast twist barrels and unexpected consequences are not my idea of fun when I have 50,000 psi (+/-) going on right next to my face when I shoot a rifle.
</div></div>

Robert, what's your experience with gain twist barrels? Say a 6.5 that is a 1/8 to a 1/6.5 ?

 

[rcw3]

Re: Is 1:8 twist too fast for .308?

I have not used that combo (i.e. 6.5 mm 1:8" to 1:6.5") but I have a number of gain twist rifled barrels and have used them for customer builds as well and they have worked out very well.

If I needed to go faster than a 1:8" twist in a 6.5 mm barrel, I would use one for that. Bartlein will speed the twist up by 1" for a flat charge, but if you go over an inch of tighter twist then additional charges come into play. So far, I have stayed within that 1" of additional twist up. I don't know what twist you need to wind up at, but I don't know of an application where you would need a 1:7" twist for 6.5 mm bullets (unless it's something like those specialty high B.C. solid bullets turned on CNC machines).

The gain twist barrels are perfect (in my view) for those very high twist applications where you want to be assured you are not going to put yourself into a potentially unexpected situation with pressure with certain loadings.

 

[nmcclure]

Re: Is 1:8 twist too fast for .308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rcw3</div><div class="ubbcode-body">I have not used that combo (i.e. 6.5 mm 1:8" to 1:6.5") but I have a number of gain twist rifled barrels and have used them for customer builds as well and they have worked out very well.

If I needed to go faster than a 1:8" twist in a 6.5 mm barrel, I would use one for that. Bartlein will speed the twist up by 1" for a flat charge, but if you go over an inch of tighter twist then additional charges come into play. So far, I have stayed within that 1" of additional twist up. I don't know what twist you need to wind up at, but I don't know of an application where you would need a 1:7" twist for 6.5 mm bullets (unless it's something like those specialty high B.C. solid bullets turned on CNC machines).

The gain twist barrels are perfect (in my view) for those very high twist applications where you want to be assured you are not going to put yourself into a potentially unexpected situation with pressure with certain loadings.</div></div>


That's exactly what I am shooting. I am have good amount of the CNC solid bullets with the .597 bc. I need 30 hour days so I can get out and try them !!

 

[garyatlp]

You can have too fast of a twist. Here's two reasons.
Bullet imperfections are more pronounced the faster you spin it so accuracy can suffer.
Also you could spin a bullet fast enough to come apart.
Have several bullets that I found I can't use in a 7" twist .223 because they blew up before reaching the target.
Nosler 55 Ballistic Tip, Speer 52 hp, and 60 grain soft points with jackets made from .22lr cases.
The bullets you would potentially have problems in a 8" .308 would be light varmint type bullets fired at high velocity.

 

[Bandit320]

Narco thread: Almost 10 years since the previous post.

 

[epeet]

I have a 16" .308. I wish it was a 1:10, but if I wanted to try to shoot subs, I wouldn't blink at getting a 1:8. That said if I wanted to shoot .30 cal subs I'd just run .300 Blackout. I shoot mostly 168, and it shoots fine. It is way less forgiving with bonded hunting rounds. Anything not super concentric shoots like a shotgun, because you are overtwisting the problem, but target stuff is fine. The only other place the overtwisting rears its head is when you start trying to shoot at distance - the spin drift gets a little extreme, but at least it can be calculated.

 

[n2ishun]

Narco thread: Almost 10 years since the previous post.

Yea maybe....but Gary is spot on.
You can certainly overspin a bullet.
Not many thin jackets will survive 300,000 rpm.

Gary, you mention bullets having 22lr cases as jackets ?
Are you the only other Corbin bullet swage owner on the planet ?
They rock....have no idea why they aren't more popular.

 

[garyatlp]

Yes, I was aware it was old but there was inaccurate info posted and it bothers me when I think about someone who doesn't know any better taking potentially bad advice. Obviously some people are still going to read it.

Don't swage myself, I bought them from someone online many years ago for $4 per 100. Thought the headstamps on the base of the bullet was neat. But I just couldn't use them and sold them to a buddy with a 22-250 who just loved them. Super accurate for him and held together, the 52 grain Speers too, and explosive on gophers.