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Posted: 6/16/2004 11:56:04 AM EDT
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I need some help with a new build. When a round is fired, it acts as if the bolt isn't moving completely back, so with another round in the magazine it attempts to feed it but has not ejected the fired round completely and jams the new round against the bottom of the old one. With no round in the magazine the bolt does not lock open, but the fired case stays in the chamber. It's no problem manually ejecting by operating the charging handle. The fired cases are not sticking in the chamber. I THINK that it's short stroking. It's semi-auto only. Here are the specs: New Fulton slick-side large hole upper SP1 lower New M16 bolt/carrier assy. (CDNN Colt take off) Colt M4 'H' buffer in Fiberite sliding stock New 11.5" CMMG M4 barrel w/4.5" Bushy Shorty FH Several new and used GI magazines Fed. M193 and Win. Q3131A ammo Anybody had a similar problem with a similar setup? Have you fixed it? I've read everything that I could find on this forum (some of it doesn't seem to be acessible), and tried the search function with no avail. Any help with this problem would be greatly appreciated! |
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The bolt does not lock open after firing a single round with an empty magazine in the carbine. It appears to me that the fired case is being partially extracted and then re-chambered when there isn't another round in the magazine on the way up to jam it. With a round in the magazine the fired round extracts, but not fully, and does not eject. After firing a chambered round the bolt moves rearward about half the proper distance and extracts the fired case enough to allow the round that is coming up from the magazine to jam the fired case against the top of the upper. I must drop the magazine and then turn the carbine on its side to shake out the fired case in order to clear it. I can extract and eject a fired case or a live round from the chamber by operating the charging handle with no abnormal effort. The cases are thrown clear in a normal manner. I have a set of headspace gauges, it checks OK. The rim of the fired round shows only normal extractor marks. I've had other AR15s that have had tight rough chambers where the cases stuck and the extractor jumped over the rim pulling brass with it. I don't see those symptoms here. The chamber is chromed, and appeared very dull, but I really couldn't see any roughness with the naked eye. I spoke to CMMG this PM and they advised me to polish the chamber, which I have just done. They said that this has been the most common cause of this problem reported to them with this barrel. I'll take it to the range in the AM, and post the results tomorrow. I appreciate your help. |
(I'm almost afraid to ask), how did you polish the chamber? And, forget about loading more than one round in the mag until you get the rifle full stroking (bolt locking back after the last round has been fired), all you will be doing is bending/distroying ammo. |
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Fixed! Dano523 - I smiled when I read your comment about polishing the chamber.hat I first fashioned a makeshift lap using a .38cal. wool mop loaded with JB paste attached to a piece of an old sectional cleaning rod, and powered it with my Makita. I went very slowly, examining the progress until I thought that it was ready for testing. After the obligatory clean-up I took it to the range this AM. The first shot functioned properly, but I noticed that it would start to act up after getting hot, so I figured that I was on the right track and took it home to further work on it. This time I got a bit more aggressive and cut a strip of fine crocus cloth and wrapped it around a fresh bore mop, lubed the chamber with just a drop of Kroil and got after it with the Makita power again. I went very slowly, changing the crocus cloth and closely examining the results frequently. This time I was too lazy to take it back to the range, and because I live in the country where it's legal to shoot, and realizing that my closest neighbor was out of town, I tested it from my back porch. It works just fine! Many thanks to Dano523 and to Tweak for their answers to my post . |
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KClapp - Yes, I'd have to say that it was a rough chamber, as I made no other changes to this weapon during this ordeal. As I stated earlier, I've encountered a rough chamber before but its symptoms were much more obvious, such as the cases stuck so badly that I had to use a steel cleaning rod to knock them out and the extractor tearing large chunks off the rim of the fired case. This one was more subtle. A good learning experience! |
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