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Posted: 4/8/2005 9:53:43 PM EDT
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I am having a problem with my upper: I have a DPMS dissipator barrel that I had ADCO turn down and rebuild on a CMT upper. The bolt and carrier lock home fully when there is no round. However, when I try and chamber a round, the bolt will not close home. I tried several different rounds, let the charging handle slam home, used the bolt release and applied serious forward assist. I know that enough forward pressure was applied as the rifle had to be dissassembled and the bolt had to be nearly pounded out to eject the round. Quite simply, the bolt will not seat a round but closes fully and easily without a round. If this were any other rifle, I would assume that I have a serious headspace issue. In fact, one of my shooting partners said all that need to happen is to have the "un-screw" the barrel nut a few click and this should do it. However, I have recieved conflictng advice from others who say the barrel nut can't be moved. Anyone got any ideas??????? |
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I am not sure I know what the 40 degree test is---at least by that name anyway. I think the problem is with the bolt. I took my bolt carrier and bolt out of another older ar and put it into the one giving me problems and everything worked fine. I am going to go and pick up a set of headspace gauges to make sure this older bca/bolt group is actually safe with the new barrel assembly. The interesting part is that when I put the troublesome bolt and carrier into the older ar, it would close on a round but it took more pressure than it should have. It also took a ridiculous amount of pressure to pull the charging handle back and clear the round--took a light tap with a small brass hammer in fact. Anyone know what could be going on??? I changed the extractor and extractor spring and that didn't help. This bolt only has about 100 rounds on it. Is it possible it just needs to be broke in more? I checked for burrs on the lugs and couldn't find any. Thanks |
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I think I've figured it out--at least sort of. I swapped bolts between the new rifle that was worked on and an older one I had. I checked the headspace on both and everything was OK. Both rifles then functioned fine. However, the new bolt out of the new rifle was still a little tight even in the older rifle. As near as I can figure, the new barrel and bolt were barely within specs as to headspace when I purchased the upper and when the barrel was re-torqued onto the reciever, the headspace went out of spec----just barely, but enough to prevent a round from seating. Like I said, that is the only thing I can figure. The old bolt headspaces with the new barrel and functions and the new bolt headspaces and functions with the older barrel (but is still tight). Anyone see anything or any problem I might be overlooking with this solution and evaluation of the problem??? |
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