How short an AR15 bbl with a can?

[fizassist]

Hi Folks,

I have an 16" M1S 1-8 .300 Fireball bbl. I have moved the gas port to the pistol position. I have a .308 can inbound that I would like to use on this upper full-time, and I would really like to cut the bbl down to maintain an effective bbl length (with can) of 16-18". The .308 can is about 9" long. I already have a registered SBR lower.

How short do you think I can safely cut the bbl and still have it function 100% with the can on? The can should provide a lot of backpressure, so I would naively think that cutting it back to 8" or so would be fine.

Thanks,
fiz

[Scoop]

Don't know about 8 inches. May be a bit on the short side. Seems like I read somewhere that below the 9-10 inch range things really become part science, part voodoo as it relates to reliable subsonic functioning. I have an Olympic w/pistol position gas port and it runs just fine at 10.5 with subsonic loads. For what it's worth, it's reliable with or without the can.
http://www.hunt101.com/img/433084.JPG

[dflicker]

I'm working on a similar project, using a 7.5" barrel with a Leitner-Wise piston upper and Jet suppressor. One advantage I have with this upper is that the gas system is self regulating, meaning it uses only as much gas as needed and expells the rest under the handguard. You can view an animation of the system here: http://www.ar15.com/forums/topic.html?b=2&f=171&t=152504

Leitner-Wise will be putting considerable engineering effort into this gun with the intention of offering it as part of their product line. We expect to have it ready for demo at SHOT 2007 in January.

David