CMMG AR-15 Conversion kit cracked chamber adapter

harbl_the_cat

harbl_the_cat

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My CMMG AR-15 conversion kit has a crack in the chamber adapter. I hear this is actually a very common problem with them, especially with Norinco CQ556's.

Here is my theory why. I believe the Norinco CQ556 is chambered in 5.56, instead of .223. I have a theory that the CMMG was originally designed for .223, and so the case adapter has a .224 diameter. This means that the case adapter is unsupported in the Norinco CQ's chamber.

.22lr being a low pressure round, I wouldn't expect the adapter to break immediatly, however over time, the chamber simply cannot take 10's of thousands of low pressure rounds going through it, so it cracks.

This is based on the assumption that the CQ is 5.56 instead of .223 - so can anyone confirm?

Here's another dillema - can you "thicken" the chamber adapter for the CMMG conversion kit somehow, so it's not unsupported and potentially to increase it's life expectancy? I'm thinking using my wife's clearcoat nail polish, but don't know how well that will work out for me.
 
I like the creative problem solving, but I would not try the nail polish. At best it would cause sticky extraction when going back to .223, and at worst might require a hammer to get the CMMG kit out when you are done. That said, residue should be nothing a little acetone won't fix. Give 'er if you are braver than me...

I'm getting the parts to make a dedicated upper for mine. A proper twist barrel and no adapter is the way to go in my mind.
 
True enough - but does anyone really buy one of these CMMG kits for hardcore accuracy - or to go to the range and shoot off a brick for the day?

Does my reasoning make sense - and if so, what's the remedy to fix the problem? As absurd as it sounds - how about potentially wrapping the adapter with tin-foil, just to get a "snug" fit?
 
harbl_the_cat said:
True enough - but does anyone really buy one of these CMMG kits for hardcore accuracy - or to go to the range and shoot off a brick for the day?

Does my reasoning make sense - and if so, what's the remedy to fix the problem? As absurd as it sounds - how about potentially wrapping the adapter with tin-foil, just to get a "snug" fit?
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Wouldn't repeatability be a problem with a wrap of tin foil though? Each time you have to remove the kit you're basically ruining the foil.

From what I gathered there are two versions of the chamber adapter: one has a weld and one is a single piece. Apparently CMMG replaces the cracked welded ones without a fuss in the US.
 
Matt_mg said:
From what I gathered there are two versions of the chamber adapter: one has a weld and one is a single piece. Apparently CMMG replaces the cracked welded ones without a fuss in the US.
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I read they did a run of them that have failed. I heard it had to do with poor metal in that run. I don't think the chamber of the OP's gun is the issue.
 
That's what I've read on the issue as well. I think the chamber has nothing to do with it.

41 Colt said:
I read they did a run of them that have failed. I heard it had to do with poor metal in that run. I don't think the chamber of the OP's gun is the issue.
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