Thread: Trouble getting 300 Blackout to shoot and cycle subs

Hi There,

I am new to this forum and keen to get some help?

I have a CMMG 300blk upper with a 16" barrel, carbine gas system on a standard rockriver LAR - 15 lower. running a MAE 30'compact suppressor.

I am having trouble getting this to cycle subsonic rounds...and even shoot subsonic rounds, I have tried hand-loads(as below) and factory 208gn A-Max.

The hand-loads were 220gn sierra MK projectiles, small rifle federal primers, using ADI AR 2205 powder ranging from 9.0gn - 10.0gn I loaded in .1 increments, the only one that went sub was the 9.0gn the rest were super and non of them ejected. I am struggling to get the velocity low enough to be sub with enough gas pressure to eject the round.

208gn Factory load went sub and ejected but would not pick up the next round properly. (see attached)
for some reason the bolt was on top of the next round?????? is this Gas or a Mag issue?

I fired one round with the mag in and the bolt wont hold back so i'm assuming i'm not getting enough gas?

I have measured the gas hole in the barrel which is 0.112 of an inch, the inside diameter of the gas tube is 0.125, is it possible to drill the hole bigger in the barrel to give me more gas? what is the max diameter you can have without over pressuring?

can someone please help? not sure if I have a chamber/barrel issue causing not enough gas? or do I need to shorten my barrel and run a pistol gas system? I have also thought of changing to a lighter buffer spring but concerned how this would run on the super rounds?

I want my cake and to be able eat it as well, I want too shoot both sub and super while being suppressed on my 16 inch barrel.

Any help would be much appreciated!

Cheers,

Hadyn