View Full Version : SBR AR...what length barrel?

February 10, 2008, 09:53 PM
Is there any difference in reliability between a 10.25" or 11.5" barrel? Which do yall prefer? I've read different places that a 14.5" would be better but I wanna go a little shorter than that. Thanks

February 10, 2008, 10:12 PM
You'll have a hell of a time getting the 10.5" to run. Be prepared to do some tweaking on the gas system. Now, all that said, if you get one someone has already tweaked, then you would be GTG.

February 10, 2008, 10:15 PM
What about the 11.5"...do you have to adjust the gas system on them too?

February 11, 2008, 12:21 AM
Either way, you may have to open the gas port up a bit. The only way to know for sure is to try it. I have a friend who has a 10.5 on a RR M16 and he played hell trying to get it to run. He ended up opening up the gas port and adding a pigtail gas tube. It'll be a little better on a semi, but you may need more gas to operate the bolt.

February 11, 2008, 12:32 AM
Well, it's going on a full-auto machine gun lower. I'm gonna go ahead with the 11.5" and play with it as needed. Thanks

Zak Smith
February 11, 2008, 02:35 PM
There are plenty of 10.5's, 11.5's, and 12.5's that run just fine-- you just need to get one made by a company or builder that knows what they're doing with SBRs. A 16" or 20" can tolerate bubba-gunsmithing; an SBR not so much.

February 12, 2008, 01:30 PM
Years ago, I threw one together on a stripped, transferable PAWS lower. All the other parts came from Quality Parts, which evolved into Bushmaster. I used what they called their 10" "machine gun" barrel and the standard birdcage flash hider. Absolutely no problem with the gun running. Well, the first bolt group didn't do so hot, but they immediately replaced it. I've had to replace a broken extractor and a few gas rings, but other than that, the gun still runs as good as ever. I do have to keep the bolt oiled and after 200 rounds, spray it again to keep it from jamming. Maybe I just got lucky. At that time, I was mad because the lowers jumped form $200 to $400 back in '86.

February 12, 2008, 05:13 PM
I wan't to echo what Zak said. I assumed (possibly incorrectly) that you were going to be building this upper from scratch. If you are going to buy one already built, and you buy from a reputable builder, you should have no problems from the get-go.

February 12, 2008, 05:17 PM
No, I'm ordering a complete CMMG 11.5" upper. Thanks for yalls replys.

February 13, 2008, 02:18 AM
There are AR gas tubes that wrap around the barrel a couple of times to slow down the gas getting to the chamber.

I'd do a 10.5" barrel and turn it into an AR pistol...cant beat something like that! :D

February 13, 2008, 10:23 PM
There are AR gas tubes that wrap around the barrel a couple of times


You must mean the M16 pigtails....they are coiled, but don't wrap the barrel.

February 14, 2008, 01:31 PM
On my M16, I've used 3 different barrel length's so far. A 11.5" Bushmaster ran great with no tweaking, a CMMG 10.5" ran, but would just barely kick the brass out of the ejection port. I had to open the gas port to .093" which is a Colt spec. Now it runs great and it's the upper I'm sticking with.

I also used a 7.5" Model 1 barrel that seemed to be a little over gassed, if you know what I mean. I managed to make it run good by using a heavy, 9mm buffer. Now I just use my 7.5" with a .22 LR Ciener M16 conversion.

CMMG makes a good upper and you should be happy with it but if you have to do a little tweaking, it should'nt be that big of a deal. A lot of times it's just getting the correct buffer weight.