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View Full Version : CMMG 6.8mm Upper Wont Eject


valleyheat
03-17-2012, 5:14 PM
Just built a new AR. CMMG 6.8mm Gas Piston Upper, Magpul STR Stock, DPMS Lower/LPK, Magpul Miad grip, Leupold VX-R 1.25-4x20mm Pigplex.

Everything works fine and shoots accurate. However it wont eject the spent shell. First day shooting, I even had issues manually ejecting as the BCG seemed to be jammed. A little wiggle and it'd finally eject. Then it would jam to the point where I would have to break apart the upper and lower to be able to pull the bolt back and release the spent shell.
Second day, after lubing everything up again. Same issue, but at least now, I am able to pull the bolt back after each shot to eject and reload. Tried shooting with no mag and still nothing. Bolt moves back a half inch, but thats about it.
Not familiar with how to adjust gas, took apart handguard and dont see any indications of a leak. Any suggestions?

cayotehunter
03-17-2012, 5:38 PM
I would try either an adjustable gas block or a different buffer spring first. If that doesnt help contact cmmg

AK all day
03-17-2012, 5:46 PM
What about your gas rings, three piece?

valleyheat
03-17-2012, 5:53 PM
any suggestions on a adjustable gas block or buffer spring?
not sure about the gas rings, is that in the bcg? if so, yes, its 3.

Speedpower
03-17-2012, 5:58 PM
It's a Gas Piston operated correct? so why suggesting an adjustable gas block?

cayotehunter
03-17-2012, 6:02 PM
It's a Gas Piston operated correct? so why suggesting an adjustable gas block?

sorry missed that part :facepalm: nevermind on the adjustable gas block. As far as gas rings go, make sure the spaces are not lined up. In other words, the spaces in the gas rings should be staggering

Speedpower
03-17-2012, 6:09 PM
sorry missed that part :facepalm: nevermind on the adjustable gas block. As far as gas rings go, make sure the spaces are not lined up. In other words, the spaces in the gas rings should be staggering

On a piston operated AR, I don't think the gas ring matters either, as gas is not operating the bolt.

m16
03-17-2012, 6:13 PM
sorry missed that part :facepalm: nevermind on the adjustable gas block. As far as gas rings go, make sure the spaces are not lined up. In other words, the spaces in the gas rings should be staggering

Pistons cycle the action via an op rod.

You don't even need gas rings on the bolt in a piston gun.

FeuerFrei
03-17-2012, 6:14 PM
Your gas block is either ON or OFF (maybe supressed mode). Full gas is needed. NOT supressed mode.
There are no gas rings needed.
Tried different ammo and mags?
Try the upper on another AR lower for function.
If it gags again then send it back for corrective action.
If the op rod is NOT bent or broken and the bolt spring is not destroyed/bent up...send it back.
It will save time and headaches.

m16
03-17-2012, 6:15 PM
Hey OP, is your bolt carrier some kind of "anti-tilt" design?

If so, how is the fit in your receiver extension?

valleyheat
03-17-2012, 6:31 PM
wow.. feel dumb. cmmg site came back up, and I pulled the gas piston manual.. Looks like the setting was on off (guess for people with supressors to keep it more quiet by not ejecting and loading next round). Gonna take it to range tomorrow to test. Hopefully thats the fix and I can go back on working on my Rem 700.. (any suggestions on necessary mods for the rem 700 sps tactical is welcome)
Thx for the help guys.

tenpercentfirearms
03-18-2012, 6:29 AM
Also I had a customer come in telling me his Stag 6.8 wasn't ejecting the brass. Most times it just requires some lube, so I lubed it and sent it back out.

He comes back in with the same problem and thankfully the ammo too. I take a look at the box and he is shooting subsonic 6.8mm that he got on a bargain. I started laughing and said here is your problem.