300 blk won't lock back on empty

[cch2a]

Ok so I finished my 300 build and it looks super sexy but won't lock back on empty chamber no mag inserted. It's and 8" Aero barrel with a Syrac adjustable gas block and a standard weight buffer. Even with the gas block all the way open and shooting supers it still won't lock back. It will cycle a full mag but if mag is out chamber loaded and I shoot it doesn't lock back. This is my 4th rifle build using similar parts but always been in 5.56 not 300. I don't have the ability to check gas port size or drill it if needed. Could it be something else besides gas port? It seems over gassed to me with gas block all the way open but that's the only thing I can think of.

[Photoguy67]

umm you do realize the magazine has to be inserted for it to lock back? 

[cch2a]

Yeah sorry empty mag, one in chamber shoots but doesn't lock on empty mag. Don't know why I typed that the way I did lol long morning with a baby dealing with recent cochlear implants. I'm losing my mind I promise the mag was in. Edited April 9, 2016 by cch2a

[Photoguy67]

From my experience, the most common reason for a 300 black out to not lock back on last round is gas port misalignment. Are you using a 16 inch barrel with a carbine length gas system? most frustrating setup there is. 

[Dolomite_supafly]

Give me a call. We will figure this out.

[my82cam]

Dolomite is the man for the job!

[cch2a]

Sorry late reply. Got it fixed. Either gas block was misaligned or buffer weight was too heavy. My guess is gas block was misaligned. Reason I don't know is I replaced the stock with Troy PDW which uses one piece BCG buffer assembly and I reinstalled gas block. So one of those corrected the issue. Now it even cycles and locks back with 220gr subsonic unsuppressed.

[dcloudy777]

Get about a foot of so of the plastic hose they sell for aquarium pumps.  Put one end of hose over the back of the gas tube, and blow air through while aligning the block.  Perfect alignment every time.  Especially useful on funky barrels with no shoulder for the gas block.  Lining up the ports in "two dimensions" as it were gets tricky... but this method gets them just right no problem.

[Wingshooter]

42 minutes ago, dcloudy777 said:

Get about a foot of so of the plastic hose they sell for aquarium pumps.  Put one end of hose over the back of the gas tube, and blow air through while aligning the block.  Perfect alignment every time.  Especially useful on funky barrels with no shoulder for the gas block.  Lining up the ports in "two dimensions" as it were gets tricky... but this method gets them just right no problem.

Cool tip. I have a rifle (5.56) that gave me fits with locking back on an empty mag. It would also eject the brass about 1:00 position. I suspected misaligned gas block or small port. I ended up just swapping the full auto BCG with a lighter AR15 bcg, and problem fixed (well, bandaided  ). I think I'll check it like you suggest though.