Anyone know if the UBR stock is a " carbine receiver extension"? reason I ask, I am having trouble getting my 12.5" barrel, 300 blackout to cycle. It ejects, but will not pick up the next round. Neither super's nor sub's. Went to AAC's (not mine, it was custom built), and their's uses a carbine length extension. Just trying to run through the multitude of possibilities in order to get it fixed. Thanks for input. I know this has probably been beat to death.

Your buffer isnt heavy enough, it says on the AAC site that you must get an H2 buffer.


http://www.advanced-armament.com/300-BLK-Upper-125-Barrel_p_462.html

Thanks. I have tried both a standard buffer and an H2. Neither will get it to cycle. Beginning to wonder if I have the wrong spring (too heavy)in it. Not sure what I have so that may be a problem. Trying to do some research to determine. Also wondering if changing to one of those "pigtail" gas tubes will increase the pressure enough to help cycle the bolt. Again, any insight is appreciated.

Are you sure you have a carbine buffer spring in there and not a rifle length spring?

What kind of barrel is it ? Pistol gas system ?

No, I'm not sure. I'll check that out. Makes sense that the exta length could be causing me problems. My barrel is a White Oak Armament. No piston. Standard DI. Thanks for the suggestions. Keep them coming. If anyone was closer to me, I would say let's go shoot and figure it out.

I am not sure how applicable this is, but my WOA 16 inch 5.56 barrel is fairly over gassed. Not sure if that is attributing to your problem or not, but I thought it is worth mentioning. Their barrels are dead nuts accurate, but have always been intended for match applications and not suppressed applications to my knowledge.