Ar15 Barrels with 1:7 twist longer than 20" ?

[demolitionman]

I've got an AR15 that I'm wanting to re barrel with a 22" or 24" heavy 1:7 twist barrel for shooting 77 SMK's. I'm not real familiar with the platform and haven't done much with any Gas guns for that matter, but it looks as though finding a 1:7 twist longer than 20" to stabilize 77g bullets in .223 is pretty rare? Is there a reason for this? I figured the little extra bit of velocity would help past 600/700 yards. Weight isn't really a factor, the gun will be shot prone mostly using a "squeeze bag". Seems like anything beyond 20" (in .223) is a 1:8 twist and I worry a 1:8 may not stabilize a 77smk as easily as a 1:7.

Any input? Thanks guys. And fwiw I was kinda thinking of going with WOA as their prices seem pretty good.

 

[TonyTheTiger]

1:8 works just fine for 77's in every case I've seen or heard of. But so does 1:7 so if that's what you want go for it. I'd have Black Hole Weaponry conjure up the tube you want. You can choose twist and profile and a few other things while you're at it.

 

[6AYoteHunter]

I shoot the Black Hills 77 tmk a lot in a JP 22" barrel but my twist is actually a little faster than the stated 1 in 8. More like a 1 in 7.7 twist. Most boxes chrono around 2840 fps.
Built an AR for my father with a WOA 20" 1 in 7 barrel that is just as accurate but is a little slower. Think it was 2770 fps.
Both are able to make hits easy on steel at 800 yards.

​​​​​​Think that 26" woa barrel would be really cool to test. With a +2 gas system and longer barrel the fps gain should be impressive.
You could run the stability calcs on JBM ballistics and see if that setup will work where you shoot.

 

[longshot2000]

that can be done, if the gun is purely a bench gun. In fact, many 5.56 target guns are 24" or longer. Not real practical for anything other than target shooting prone, but that is common enough. As far as stabilizing a 77 grain bullet, you don't need a long barrel for that. I shoot Black Hills Mk262 as well as 77 grain tipped ammo, and there is nothing better for accuracy at distances beyond 450 yards. I agree that 1:7 is probably best. 1:8 is still going to be good. You should look at the velocity of this round at various barrel lengths. Above 20" you get to diminishing returns on greater velocity, but certainly, 24" is a little better than 20". The issue is that you will need an every heavier profile barrel, and will then need an even more reinforced upper receiver and assembly to hold the barrel stable.

 

[JMcBurn]

Columbia River Arms will make a 20-24" barrel in 1-7 twist

 

[Bigjake83]

http://www.accurateandreliablerifle.com/products.html

 

[redneckbmxer24]

People get way too wrapped up in twist rates. A 1:8 will stabilize a much longer bullet than you'll ever get in an AR mag, really anything that is optimal for the 223 round even. The 90's typically like a faster twist but they run so slow in a 223 I don't think they're worth it and you're going to need to single feed in an AR which is pretty pointless.

You'll have no issue with a 1:8.

 

[demolitionman]

People get way too wrapped up in twist rates. A 1:8 will stabilize a much longer bullet than you'll ever get in an AR mag, really anything that is optimal for the 223 round even. The 90's typically like a faster twist but they run so slow in a 223 I don't think they're worth it and you're going to need to single feed in an AR which is pretty pointless.

You'll have no issue with a 1:8.

copy that. Like I stated, I'm set on 77SMK's and have 1000 of them on hand so I am going to have to make them shoot, and therefore I really didn't want to chance anything with the twist rate. Thanks for your reply Bmx'er.

 

[redneckbmxer24]

copy that. Like I stated, I'm set on 77SMK's and have 1000 of them on hand so I am going to have to make them shoot, and therefore I really didn't want to chance anything with the twist rate. Thanks for your reply Bmx'er.

No problem.

Also keep in mind that stability becomes more of a concern in shorter barrels vs longer as the shorter barrels will run lower velocities increasing the possible need for a faster twist to stay stable. In an AR15 you're good with anything .224 that you can run mag length with a 1:8 even with shorter barrels. Most longer (even some 16") barrels with 1:9 will also do the trick but you're chancing running on the line of marginal and it doesn't always work with the 77's. 1:9 is fine with all the 69's and lighter though.

You're good to go though. Another heads up, you may want to check out the Ballistic Advantage barrels. I recently picked up a few, one being a 18" SPR 223 wylde for about $150 and it shoots lights out. I've had a Proof SS on backorder for months now and bought this to get me running for a match but I don't even know if I'll even swap it when the Proof comes in. So far I only ran it with a generic 77gr Nosler CC/Power Pro 2000MR load I developed that shoots well in several rifles but I've got Berger 77gr OTM's being delivered tomorrow to work up a load with. I don't know if they make them in longer lengths, but they are great barrels.

 

[padom]

I run both 1:7 and 1:8 20" WOA and Rainier UltraMatch barrels. Ive been shooting 77smk with 23.6g 8208XBR at 2801 with single digit SD's for a few years. You will have zero issues with 1:8 at all.

 

[Greg Langelius *]

Your choice at Lothar-Walther. Please note that matched bolts are often included in the asking price.

Greg