Posted: 2/4/2012 5:36:22 AM EDT
bought a complete upper (20 govt profile barrel) from them, failure to feed issues it was short stoking. They did take it back test fired and sent it back said it was OK. It was not. I had to fix it myself, seems ok but still has a problem with 62 grain ammo. wpould not buy from them again.
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No I am not an ar15 armorer or even an expert (but I am learning with this rifle), that is why I elected to buy a complete upper from CMMG. Tried different ammo both miltary 5.56 and.223 bunch of different magazines and two different lowers (Stag and Bushmaster), same issues. First round would chamber and fire, next round would eject next round would not feed. When I loaded only one round into a magazine it would load, fire but the bolt would not be held open. This lead me to believe it was short stroking for some reason.
1) changed buffer spring and buffer, no improvement 2) checked gas key, it was tight, staked and did not seem like it was leaking gas from where it mates to the bolt 3) replaced gas rings, no improvement 4) checked for to make sure the bcg moved freely, noticed that it seemed to rub on the gas tube, repositioned (bent) the gas tube. also this rifle has a front clamp on gas block removed it, made a pin to line up hole in barrel and hole in gas block, assembled it, scribed alignment lines, removed gas block, removed alignment pin, reassembled rifle. 5) test fired and seemed to function better (no short stroking), have about 400 rounds through it, like I said still has an issue with 62 grain military ball. My other AR 15s will shoot anything I put in them, just figured this one should do the same. any suggestions are appreciated. Not trying to bad mouth CMMG, they did take the upper back and look at it but I still had the same issues with the rifle. |
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OK, thanks so much for the additional information, it helps!
It does sound like short stroking for sure. Since you have cycled the action by hand and it now moves freely we can rule out mechanical drag. That means one should make sure the gas system is working fine. I have seen the gas blocks not properly aligned. This cuts back on the gas supply and will make it a bit wimpy when fired. Another problem, not so common, is the gas hole in the barrel is not large enough, as in restricted by a burr or some debris. I take it you checked that when you took the gas block off. Another problem I have heard of (haven't seen myself but heard its possible) is that the gas tube itself is restricted. But, we need to look at the entire gas system from the time it leaves the barrel via that little hole until it is inside the bolt where it pushes the bolt apart from the carrier. Did you by chance take the bolt apart and look inside at the gas rings? Make sure they are free to rotate and that the ends are NOT lined up and that they have some tension against the bolt carrier so they can seal properly. Assemble the bolt group and insure it has some tension from the gas rings but will also move freely with the rings installed. Anything is possible. I mean, it could be something really rare like you got the only weak ammo in the world...again, not likely but since you sent it back and they tested it either there is something else going on with the ammo...or....something happened when they tested it. Either they are using kick-butt powerful ammo, or the upper got mixed up in the testing process. Clearly something is going on. Have you called them back and inquired about this, letting them know exactly what is going on? Did you fill out the on-line warranty claim on their web site to let them know about this? I can not tell you what is wrong with your rifle without seeing it, but I do know the people at CMMG will make it right if you work with them. I know this is frustrating to deal with when its YOUR gun and you are in the middle of the problem. No one likes to be where you are. I know....been there a few times myself. BUT, the good side of this is that when its over you will have a much better knowledge of your rifle and how it operates. I know that may not mean much right now, but down the road you will benefit from the experience. I know...I have learned many a good lesson in life from over coming problems that frustrated me at the time. Keep us informed, we want to know how this works out. |
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Yes I checked the gas rings, actually replaced them, staggered the ring gaps. The gas blead hole under the gas block is the right size as far as I can tell no debris or blocks in hole or gas tube (blew out gas tube with air). Seems like a well made upper, accurate just some little issues. And yes I am learning about the rifle.
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