shortest sbr 300 blackout that will cycle subsonic

[jdasilva]

2 questions guys:

1)
I'm about to sbr my 300blk ar15 & wanted to know what the shortest barrel I can use to cycle subsonic ammo without a silencer.

I have 762 silencers but sometimes i like to shoot unsuppressed, a lot of times, subsonic ammo is all I can get my hands on.

No matter suppressed or unsuppressed, I want my rifle to cycle reliably with any factory ammo I have available.

I currently do not reload & I've looked all over for this answer but no dice.

2)
If by chance the shortest barrel is 12.5", can I just cut down my existing barrel with a carbine gas system?

I was looking to either do that or get a 8"-10.5" pistol barrel, but I can cut & thread it myself.

[curtistactical]

The shortest I have gone is 7" with pistol gas system and the gun worked flawless. This leaves plenty of time for the gas to do its thing. Anything shorter I really don't know but am interested to hear if anyone has experience with it.

[RPM509]

I have two, one 8" and the other 10.3", both with pistol gas length, both run fine suppressed and unsuppressed.
Think AAC developed it to run under a 8.5 - 9.5 barrels right?

Simple fix if you go shorter, just open the gas port up a little bit until you get reliable cycling.
There is a point of no gain though, what it is I don't know.

[L1A1Rocker]

The 300blk loves to run as an SBR. AAC went with 9 inch and Novesky went with 8 inch on their factory setups. I've got a home built 8 inch that runs fine. My next SBR that I'm working on will be 7.5. IIRC some have got to 6 inches before any problems begin to show.

Robert set up a sister site to this one that is just for 300blk stuff. Be sure to check it out as your login for here should work there as well: http://300blktalk.com/

[jdasilva]

Thanks for the replies, What about with carbine length gas?

[L1A1Rocker]

Thanks for the replies, What about with carbine length gas?

Oops, sorry bout that. If the barrel is less than 16 inches it must be pistol length. I'm in the same boat on that. I've got a spare 16 inch barrel but I cannot cut it down because it's carbine length gas port.

[Bendersquint]

6.5" with pistol gas port. Sewing machine.

[jdasilva]

nice!

[curtistactical]

Its no big deal to change the carbine gas port location. I had Wicked weld over the carbine gas port then just machined the barrel back and put a pistol gas system in it. The carbine gas system only works reliably on 16" if you are shooting super sonic ammo, subs will cycle but not reliably. I use pistol gas system on 16" and shorter.

[dan9591]

I'm running a 6" with an slr rifle works adjustable block. Runs everything suppressed and unsupressed.

[Bendersquint]

Its no big deal to change the carbine gas port location. I had Wicked weld over the carbine gas port then just machined the barrel back and put a pistol gas system in it. The carbine gas system only works reliably on 16" if you are shooting super sonic ammo, subs will cycle but not reliably. I use pistol gas system on 16" and shorter.

I had a 300Whisper 16" upper that ran thousands of subsonics only and never a hitch, ran a carbine gas port.

I think it depends on who makes it.