Posted: 9/22/2012 8:11:16 PM EDT
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I have an CMMG M4LEPII that I've never had a problem with. Not one malfunction the entire time I've owned it. Today at at match I had it stove pipe on me 3 times. It dawned on me pretty quick when it starting happening that I had done two new things with the gun. I had A: dissembled an cleaned the ejector for the first time in a while, and B: I started shooting a new batch of ammo.
So for the rest of the match I nursed what little Fed AE .223 I had left. I was running low and had to burn 6 rounds of the 5.56 then I almost got DQ'd because I dumped the gun with a round still in the chamber, even though I had dropped the match and cycled the charging handle at least twice. But yet when the RO pulled back the charging handle it popped right out. 
Since I bought this gun I don't think it has a single round through it that wasn't Federal American Eagle .223 except for a box of Federal AE Tracers on the 4th. I had just recently picked up 500 rounds of Federal XM193 brown box from Cabela's. Like and idiot I went to a competition with having never tested it in this rifle. The ejector looks fine (didn't take any close ups while it was off)  
This is the first time I've had 5.56mm in this rifle. I almost eclusively shoot black box Fed AE .223 through it. 
Having never held the two together I never realized they were so different, round is longer and the neck is slightly different. The fit in the magazine is more drastic that I'd thought too.  
If this all looks normal to you... any idea why this round would stovepipe more where the Fed AE .223 does not? |
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From what I know stovepipes are caused by weak ammo, oversprung gun or bad extractor. You could have gotten unlucky with a bad batch of ammo. Also, CMMG's have a reputation for having tight chambers, it might be too tight of a fit for the slightly larger 5.56. My cousin, who owned a CMMG said his barrel was marked 5.56 but when measured was a really tight .223 chamber.
I would: 1. Try the ammo in a different rifle 2. Change out the extractor if the ammo is not the problem, if the problem persists, I would say it is because of the tight chamber |
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Hmm... I was actually thinking it was hotter and causing the bolt to move faster, but that could be too. Was going to try a H3 buffer I think I have and see if that makes any difference.
Will probably try this in my boss's gun and trade bolts with him (he has a AA piston gun) see if we can find any common cause. |
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Quoted:
Hmm... I was actually thinking it was hotter and causing the bolt to move faster, but that could be too. Was going to try a H3 buffer I think I have and see if that makes any difference. Will probably try this in my boss's gun and trade bolts with him (he has a AA piston gun) see if we can find any common cause. I don't think a faster moving bolt will cause stovepipes as the extractor should still work fine. I'm really leaning towards the tight chamber issue as I'm thinking the extractor is letting go too early, because of the extra force required to pull the casing out causing it to not extract all the way causing the stove pipe. And when you racked the rifle the extractor was just letting go of the casing as your hand doesn't have the sudden force the piston has on the BCG. The RO might just have pulled it the right way to not cause it the let go. But don't take my word for it as I am no super expert, I'm just basing it off of what I understand of the platform. |
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I agree with EvilBetty,
5.56 is going to be hotter usually than .223 Sami loads. As you noted the case is a wee bit larger also, so it will not spring back as much. Giving it more hold onto the walls of the chamber. I have seen 5.56 mil surp fired from a .223 chamber. Everyone of the primers where backing out with soot rings between primer and brass. Evil did you look at any of the fired brass? What did the primers look like compared to the A.E. rounds? Marks on the brass from the extractor? I think your barking up the right tree with the extractor jumping the extractor rim on the brass. Think the only reason the RO got the brass to come out is cause it had cooled down as the chamber cooled enough to allow it to slip back out. |
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Quoted:
2000 rounds and counting. 
Never a malfunction until I loaded this ammo.
I clean rather meticulously, but some credit has to be given to the piston system though. Never really anything in the receivers but brass flakes. I have dog hair, carbon build up, bits of cheez-its, what looks like some sludge.. hmmm |
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Quoted:
Quoted:
2000 rounds and counting.
Never a malfunction until I loaded this ammo.
I clean rather meticulously, but some credit has to be given to the piston system though. Never really anything in the receivers but brass flakes. I have dog hair, carbon build up, bits of cheez-its, what looks like some sludge.. hmmm That's all? |
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Quoted: Hmm... I was actually thinking it was hotter and causing the bolt to move faster, but that could be too. Was going to try a H3 buffer I think I have and see if that makes any difference. Will probably try this in my boss's gun and trade bolts with him (he has a AA piston gun) see if we can find any common cause. That is my thought as well, at least from my side of the screen.  The only cartridge dimensions that should have any actual functional effect between 5.56 and .223 are the bullet leade, with the 5.56 having a longer leade. Are you sure you got all the crud out of the ejector channel when you cleaned it? Perhaps the roll pin got boogered a bit and the ejector is catching on it? Does your extractor still have the "kittens teeth" feel to it? When you run your fingers over the claw, the corners should feel like little kitten's teeth. Kind of sharp, but not so much as to cut you. Is there an O-ring around the extractor spring? The bolt looks kinda dry too. |
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Quoted:
Quoted:
Hmm... I was actually thinking it was hotter and causing the bolt to move faster, but that could be too. Was going to try a H3 buffer I think I have and see if that makes any difference. Will probably try this in my boss's gun and trade bolts with him (he has a AA piston gun) see if we can find any common cause. That is my thought as well, at least from my side of the screen.
The only cartridge dimensions that should have any actual functional effect between 5.56 and .223 are the bullet leade, with the 5.56 having a longer leade. Are you sure you got all the crud out of the ejector channel when you cleaned it? Perhaps the roll pin got boogered a bit and the ejector is catching on it? Does your extractor still have the "kittens teeth" feel to it? When you run your fingers over the claw, the corners should feel like little kitten's teeth. Kind of sharp, but not so much as to cut you. Is there an O-ring around the extractor spring? The bolt looks kinda dry too. Extractor seems fine, it does have that kitten tooth feel. I checked the spring and o-ring, checked for any brass flakes that could be jamming it up, it all looked fine. Bolt was sans lube for the photo op post cleaning. The buffer (as well as my spare) are both 3 oz. Going to try a H2 or H3 this week if I can make it to the range with this forecasted rain. |