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Posted: 7/10/2009 4:54:03 PM EDT
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I recently put an upper together, and the upper receiver itself appears to be slightly out of spec. The bolt carrier binds slightly when it is at the rear of its travel. Without any lube, it is almost enough to keep the carrier back without the bolt release being engaged. When the carrier is well lubed it moves pretty freely, but you can still feel it trying to bind at the rear of its travel. I have switched out other carriers, and charging handles, and the issue is definitley with the upper. I have put about 50 rounds through it without any malfunctions, but I made sure to keep the carrier slathered in slip 2000.
I was thinking that if I shot it enough, it would smooth itself out. Does anyone see a problem with this line of thought? Other suggestions? I don't want to take the upper apart and send the upper receiver back if I can help it, but if the inside of the receiver and the carrier are hard enough that they will not wear in, or if wearing the parts in to this extent is not advisable, then I guess that may be where I have to go. Thanks in advance. |
| Thanks for the replies. It's not a hammer issue - the carrier sticks when it is off the lower. When I first ran the carrier in, it stuck hard enough that I had trouble getting it out. Tried other carriers, same problem. Tried first carrier in another upper, no problem. Tried carrier with no charging handle or bolt - still stuck. If there is no issue just running rounds through it until it works in, that is what I will do. I guess there really are plain few problems that can't be fixed with a suitable application of some sort of explosive. Thanks for the help. |
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If the carrier is sticking when the bolt is locked home (all the way forward), then chances are the gas key is not aligned to the carrier key. Pull the bolt off the carrier, slide the carrier into the upper all the way forward, and watch the mating of the gas tube to the key. If needed, the gas tube can be tweaked/aligned by bending it over the middle of the barrel. Also, make sure that the gas tube does wiggle some in the upper receiver. If it's rock solid, then the barrel nut was installed correctly, hence the top opening between the spines not aligned with the gas tube channel in the upper receiver.
If the problem is on the other end (carrier sticking as its way back in the action, then chances are it's the key slot in the upper track, and the key will have it's way with the track until the carrier can glide smoothly. |
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I did check the gas tube when I installed everything, and it was aligned pretty good (to use a technical term). I used a DD Lite FF tube, so no issues on aligning the barrel nut. The gas tube has plenty of play, and there does not seem to be any uneven wear on it (though the amount of shooting has been pretty limited, I manually ran the carrier about 100 times before firing it to try to work things in a bit). In any event, the carrier sticks at the rear of the travel - the choking point seems to be just to the rear of the ejection port, and seems to be lower than the ejection port, i.e., closer to 5 or 7 o'clock, rather than at the key slot in the upper track. I will look at the key slot just to be sure. I didn't notice any burs or anything noticably sticking out when I tried to pin point where it was binding, that just seemed to "feel" like where it was getting stuck (I know, more techincal terms).
It did seem to start to work itself in a bit while I shot it. The first several rounds barely cleared the ejection port - they just kind of fell out and rolled off the hood of my Jeep, though they did reset the hammer and lock back the carrier when a single round was fired - but by the time I was through 30 rounds or so, it was kicking them out at 3 o'clock and they were fliying a good 10' - 15'. Also by the end I was getting some pretty good accuracy, but was still concerned that after the fouling built up and the lube started to burn off a bit I might have reliability issues. This is the first upper I have tried putting loctite on the barrel extension when I installed the barrel (probably should have waited on that since I knew the carrier was sticking in the upper a bit before I installed the barrel), and I didn't want to have to try to pull the barrel out unless it was necessary. If just shooting the thing will work the parts in, then that is what I will do. Hopefully I'll be able to get it out again this weekend. Thanks for your time, Dano523. |
| Some folks will use Loctite on the barrel extension when they install the barrel to (theoretically) make the interface between the barrel/barrel extension and the upper receiver more stiff, thereby promoting accuracy. I have heard of guys using either blue or red Loctite (I think Kuleck/McGee's book says to use red). This is the first time I've tried it, and I used Rocksett instead of Loctite, figuring it would be more resistant to heat. I was getting some pretty good groups once things started to settle in, but I'm not sure what they would have been if I hadn't used the Rocksett. I may try it with one of my other uppers that I have already established a baseline for accuracy just to see if there is any improvement. Anyway, that is the theory behind it. |
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