556 SBR upper

[kb66]

The Soviets figured out with the Krinkov, which has an 8.3" barrel, that the very short barrels required a faster twist rate to stabilize the bullet and avoid keyholing. I would expect that with a barrel length below 10.5", a 1:7 twist would perform better. The twist rate on a 5.45x39 Krinkov, that shoots the 53 grain 7n6 bullet is 1:6.3.

 

[Trigger Time]

You could do the ranier arms super match 10.5" .223 wylde 1:8 , very good uppers!

 

[Khill]

Thumbs up on the Rainer Arms uppers. They have several options and are great build quality if you want a custom and complete upper or just good parts. I like 9.5" 1:7 twist on the short side and 12.5" 1:9 twist max length. The 10.5" is a nice compromise and either twist is fine (why not 1:8...right in the middle).

 

[mammynun]

I haven't noticed any reliability difference between my 10.5" and 12.5" DI uppers. They're both built with Rainier barrels with non-adjustable gas blocks; the 10.5 is a Select series and the 12.5" is an UltraMatch, both are 1:8 twist. Both prefer 62gr or heavier bullets from an accuracy standpoint, groups open up a little with 55gr but they're still easily minute of man to (at least) 200 yards with an Aimpoint or BUIS.

I have a 7.5" Rainier Select with a KX-5 on the front and a BCM gas block, and it's much more picky as far as functioning with all types of ammo. It's 100% reliable with M855/SS109 with a Sprinco "Blue" recoil spring and a Spikes T-3 buffer... but it's much less reliable with Federal AE .223 in that configuration (it short strokes; fired brass is weakly ejected and the next round is not stripped from the mag). if I replace either the spring OR buffer with "standard carbine" versions, it shoots the .223 reliably but the recoil pulse is noticeably more "violent" with NATO spec ammo. I'm still playing with spring/buffer combos to find the "best" balance... if I were to try and add my suppressor (SDN-6) into the mix I don't know that lt would be possible to shoot .223 unsuppressed and 5.56 suppressed without changing the buffer and/or spring.

 

[bigcraig]

If I were you, I'd build a 10.5", 1:7 twist, with adjustable gas block. Then buy at least a 13" rail that extends past the muzzle. Then buy a Saker so you can do something like this:

http://i1050.photobucket.com/albums...relSBRwithSuppressor-Sideview_zps5fc2bd0c.jpg

The pic shows a 9mm AR, there are not many hand guards that will fit a 5.56 suppressor inside them.

 

[bigcraig]

What manufacturer warranty allows a can on a 7.5 inch barrel?

Ops Inc.