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Posted: 8/20/2009 9:50:24 PM EDT
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My wife has a CMMG 1/7 M4 barrel on her gun. The bolt is a Young Mfg, with BCM extractor upgrade. She shot it at a course, it shot fine until the chamber started getting dirty (400 rds or so) cases started sticking, and the extractor ripped the rim off some brass. Yesterday, with everything cleaned and lubed and an H-buffer replacing the standard weight buffer, the mil-spec brass was still sticking in the chamber, though the extractor is just hopping over the case rim, and no longer ripping it off. I may try to find some SAAMI .223 ammo and shoot it, see if there is any difference. I am thinking two courses of action 1) trying a H3 or 9mm buffer to give more time for chamber pressures to drop (band aid solution) 2) the chamber is out of spec Its a chrome lined chamber, so the only option is to take it off the gun, and ship it back to CMMG. Is there anything else I'm not thinking of that I should try before doing that? I've built half a dozen guns before, and this is the first one I've had problems with... Thanks |
| If you pull the upper off and drop rounds by hand in to the chamber, push them down with your finger. Then tip the upper up and see if the round will drop free. If not something is out of spec with the rounds or the chamber. If you're inclined you can polish the chamber yourself with high grit paper, but if it is the chamber I'd just send it back to CMMG as they will take care of it. |
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I was right, I needed a second set of eyes. I ran it with the H buffer today. It was short stroking every 4-5 rounds. Taking it apart, my buddy noticed the buffer retainer was wearing on the bottom of the bolt carrier. We filed that down a few thousands, and the gun ran through four mags of differing ammo (M855, M193, .223 and Wolf) with no problems. I think between the couple trips to the range, the H buffer fixed the timing issue, but with the drag from the buffer retainer, the added inertia from the H buffer was too much for the bolt to overcome, hence the short stroking today. It doesn't necessarily explain why the extractor was hopping over the cases the other day, but I'll take it out again (when its not raining) and throw another couple hundred through it, and make sure its running as it should. For now, it seems to be fixed.... |
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Quoted:
My wife has a CMMG 1/7 M4 barrel on her gun. The bolt is a Young Mfg, with BCM extractor upgrade. She shot it at a course, it shot fine until the chamber started getting dirty (400 rds or so) cases started sticking, and the extractor ripped the rim off some brass. Yesterday, with everything cleaned and lubed and an H-buffer replacing the standard weight buffer, the mil-spec brass was still sticking in the chamber, though the extractor is just hopping over the case rim, and no longer ripping it off. I may try to find some SAAMI .223 ammo and shoot it, see if there is any difference. I am thinking two courses of action 1) trying a H3 or 9mm buffer to give more time for chamber pressures to drop (band aid solution) 2) the chamber is out of spec Its a chrome lined chamber, so the only option is to take it off the gun, and ship it back to CMMG. Is there anything else I'm not thinking of that I should try before doing that? I've built half a dozen guns before, and this is the first one I've had problems with... Thanks The brass that was stuck in the chamber , was it difficult to push out with a cleaning rod ? Or did it just " fall out " ? God bless Wyr |
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Quoted: Quoted: My wife has a CMMG 1/7 M4 barrel on her gun. The bolt is a Young Mfg, with BCM extractor upgrade. She shot it at a course, it shot fine until the chamber started getting dirty (400 rds or so) cases started sticking, and the extractor ripped the rim off some brass. Yesterday, with everything cleaned and lubed and an H-buffer replacing the standard weight buffer, the mil-spec brass was still sticking in the chamber, though the extractor is just hopping over the case rim, and no longer ripping it off. I may try to find some SAAMI .223 ammo and shoot it, see if there is any difference. I am thinking two courses of action 1) trying a H3 or 9mm buffer to give more time for chamber pressures to drop (band aid solution) 2) the chamber is out of spec Its a chrome lined chamber, so the only option is to take it off the gun, and ship it back to CMMG. Is there anything else I'm not thinking of that I should try before doing that? I've built half a dozen guns before, and this is the first one I've had problems with... Thanks The brass that was stuck in the chamber , was it difficult to push out with a cleaning rod ? Or did it just " fall out " ? God bless Wyr It needed the cleaning rod. |
| To me US military surplus or quality similar ammo from one of the major companies is the true acid test for reliability in a finicky AR. Try something like winchester white box, or american eagle (it is a federal product) to give your gun a fair shake. Also, make sure your chamber is truly clean, use a good cleaner like shooters choice or hoppes powder solvent. We use brake parts cleaner in the army for this, but alot of people cringe when they hear this, and dont want to use it on their guns. |
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