Looking Barrel Advice For SBR .308

[Boxcuta]

I’ve been looking for information about short fast twist 308 barrels. I’ve read a few posts that make claim of experienced folks shooting 12.5” 1-8 twist barrels really far. Practicality aside, how is this done, with what projectile? Any info would be appreciated. Thanks in advanced

 

[longshot2000]

sounds too fast to me.

disclosure: I am a rifle builder and barrel and scope nerd, but I do not build to short 7.62 SBR. I do design and build 20" 7.62 barrels and 10.3" to 14.5" SBR barrels in 5.56... That means, I kinda have an idea what you are doing, but treat my comments with a grain of salt.'

The 20" barrels that I work with are 1:10 to 1:12 for 7.62. I would not think that 1:8 in an SBR would be productive. Too much spin that also retards velocity and builds excess pressure. All that aside, why?

I am not sure why one would want to try. Longer range barrels work best with 168 to 175 gr. Mid-range barrels are often spec'd with ball ammo, at least for tactical guns, which is 147 to 155 gr (depending on who defines it). I don't spec or shoot much ball ammo, but if you think of it as the run of the mill least common denominator, you want your gun to be able to shoot ball ammo. Most of that is also in the 1:11 to 1:13 range.

 

[littlehendrick]

sounds too fast to me.

disclosure: I am a rifle builder and barrel and scope nerd, but I do not build to short 7.62 SBR. I do design and build 20" 7.62 barrels and 10.3" to 14.5" SBR barrels in 5.56... That means, I kinda have an idea what you are doing, but treat my comments with a grain of salt.'

The 20" barrels that I work with are 1:10 to 1:12 for 7.62. I would not think that 1:8 in an SBR would be productive. Too much spin that also retards velocity and builds excess pressure. All that aside, why?

I am not sure why one would want to try. Longer range barrels work best with 168 to 175 gr. Mid-range barrels are often spec'd with ball ammo, at least for tactical guns, which is 147 to 155 gr (depending on who defines it). I don't spec or shoot much ball ammo, but if you think of it as the run of the mill least common denominator, you want your gun to be able to shoot ball ammo. Most of that is also in the 1:11 to 1:13 range.

The new CSASS has a 1-8 twist barrel if I remember correctly, and is 16”. Many blackouts have that twist rate, and he will be getting a slight velocity boost over a 16” 300blk with the same given bullet weight.

 

[MtnCreek]

Is the goal to stabilize long subs?

 

[Fig]

I am not a huge .300BLK fan (even though I have a nice one), but it seems to me that if you want a .30 cal SBR this is the cartridge, and not .308 where you have humongous case capacity for little or no reason.

Then again, I've never been enamored with the idea of an SBR shooting long distance. To me the reason to chop a barrel down is to move efficiently in tight spaces; not make impacts at range. To me the point of an SBR is to make a rifle become as handy as a pistol.

 

[AK4900PA]

I'm putting together a 12.5" .308 SBR using a BCG and barrel from KAK. It's a 1/10 twist which should have no issue stabilizing anything I'd be shooting out of it.

Not sure what the point of a 1/8 twist barrel is. Only thing that would benefit you with would be subsonics in which case you'd probably want a 1/7 and it would effectively become a single shot.

 

[Boxcuta]

sounds too fast to me.

disclosure: I am a rifle builder and barrel and scope nerd, but I do not build to short 7.62 SBR. I do design and build 20" 7.62 barrels and 10.3" to 14.5" SBR barrels in 5.56... That means, I kinda have an idea what you are doing, but treat my comments with a grain of salt.'

The 20" barrels that I work with are 1:10 to 1:12 for 7.62. I would not think that 1:8 in an SBR would be productive. Too much spin that also retards velocity and builds excess pressure. All that aside, why?

I am not sure why one would want to try. Longer range barrels work best with 168 to 175 gr. Mid-range barrels are often spec'd with ball ammo, at least for tactical guns, which is 147 to 155 gr (depending on who defines it). I don't spec or shoot much ball ammo, but if you think of it as the run of the mill least common denominator, you want your gun to be able to shoot ball ammo. Most of that is also in the 1:11 to 1:13 range.

Is the goal to stabilize long subs?

The main reason I am doing this is fun honestly, I read something that made me really scratch my head, problem is I can't find any more details or the original post at this point. The idea of a short .308 seems neat to me for some reason, I realize there are better ways.

Having said that, here's a screenshot of the post that got my noggin jogging, they are discuss the merits of the 13.5 SCAR 17. Plus the Mcmillan CS5 Alias is a neat concept of course it is a bolt action.

 

[Boxcuta]

I'm putting together a 12.5" .308 SBR using a BCG and barrel from KAK. It's a 1/10 twist which should have no issue stabilizing anything I'd be shooting out of it.

Not sure what the point of a 1/8 twist barrel is. Only thing that would benefit you with would be subsonics in which case you'd probably want a 1/7 and it would effectively become a single shot.

Awesome let me know how it turns. I have no source for what I am about to say but the faster twist makes sense to me in short barrel, yes it spins faster but it also leaves the barrel sooner. I could be wrong, that's why I am here to learn more.

 

[AK4900PA]

http://www.bergerbullets.com/twist-rate-calculator/

I use this calculator quite a bit for research purposes. Not sure exactly how accurate it is, but it says a 175gr bullet at 2250fps which should be easily attainable out of a 12.5" barrel would have a SG of 1.95 with anything over 1.5 being comfortably stable. I have no hands on experience yet since my build is not complete, but unless you're worried about subsonics I think anything faster than 1/10 is going to be unnecessary.

 

[Boxcuta]

http://www.bergerbullets.com/twist-rate-calculator/

I use this calculator quite a bit for research purposes. Not sure exactly how accurate it is, but it says a 175gr bullet at 2250fps which should be easily attainable out of a 12.5" barrel would have a SG of 1.95 with anything over 1.5 being comfortably stable. I have no hands on experience yet since my build is not complete, but unless you're worried about subsonics I think anything faster than 1/10 is going to be unnecessary.

Interesting, I'll look into.

 

[atomic41]

Someone on here has had success with SBR .308s. I don't remember who and maybe they got lost in one of the moves but I remember he posted a lot about his.
I know a few guys local to me have been building them for a while but I don't know how well they have turned out. I too am tempted to play around with this.

 

[AK4900PA]

There's quite a few guys over on some of the AR-15 forums that run short barreled large frames. I was hesitant to do 12.5" .308 since I already have a 12.5" 6.5 Grendel. The ballistics between the two are very similar, but the energy on target is enough to justify it. It'll likely be my go to hog gun.

 

[Boxcuta]

There's quite a few guys over on some of the AR-15 forums that run short barreled large frames. I was hesitant to do 12.5" .308 since I already have a 12.5" 6.5 Grendel. The ballistics between the two are very similar, but the energy on target is enough to justify it. It'll likely be my go to hog gun.

I'm actually working on a12.5 Grendel myself. I starting to think about going 13.5 or 14, or whatever I can get away with using a pinned suppressor mount to avoid SBRing.

 

[AK4900PA]

My foray into the world of AR's consists of 5 uppers, but only 2 lowers. I have a SBR'd small frame lower with 3 uppers (4.5" 22lr, 6.25" 300blk and 12.5" Grendel) and a SBR'd large frame lower that will have 2 uppers (12.5" .308 and 18" 6.5 Creedmoor). Started out with the plan of building a 300blk and it got kinda out of hand, but I think it work well for covering me for a very large range of uses. The 12.5" .308 did force me to buy a new suppressor since my current titanium can isn't rated for .308 out of a barrel that short, but I'm not so sure I consider that a negative. ?

 

[Boxcuta]

Did more digging this weekend, decided to avoid SBRing for right now. Settled on a 14 inch 1-8 pinned with a Griffin Armament Flash comp since I use their cans exclusively. I'll post build details as I get more parts together.