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Posted: 2/4/2015 1:27:48 PM EDT
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Check this out.
I have this BCM upper receiver that was build into a complete upper. I take the barrel off to put a new barrel on and the threads will not accept ANY other KMR barrel nut. The barrel nut makes 3/4's of a turn and stops. The resistance is considerable, and I do not want to fuck up the upper. I tried 3 different KMR barrel nuts and the only one that will thread on perfectly is the one that was assembled onto the upper. I inspected the threads, and they look perfect. I also cleaned the threads and they still have no visible obstructions. I've built 10 or so uppers and never had this happen before. Anyone ever have this issue before? Just curious. I already ordered another upper receiver. I don't really care to fix it because it gives me an excuse to buy another upper receiver. I figure I have a dedicated upper/barrel (due to pinning and welding) combo now due to this issue. 
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| Some manufacturers use non-standard threads on their upper receivers. 1.25-18 is the standard. I've seen 1.375-18 on some polymer uppers. Perhaps that is what you've got going on here. If the upper threads are larger than standard, you won't be able to use a standard barrel nut on it. |
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Quoted:
Some manufacturers use non-standard threads on their upper receivers. 1.25-18 is the standard. I've seen 1.375-18 on some polymer uppers. Perhaps that is what you've got going on here. If the upper threads are larger than standard, you won't be able to use a standard barrel nut on it. My mistake for not being clear. I mean to say that the barrel nut that does fit is a KMR on a pinned and welded barrel. However, when I went to change barrels trying a few different KMR barrel nuts, they would not thread. Essentially, only the one KMR barrel nut works, and the others did not. Weird. Maybe I fucked up the threads somehow. |
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Quoted:
Some manufacturers use non-standard threads on their upper receivers. 1.25-18 is the standard. I've seen 1.375-18 on some polymer uppers. Perhaps that is what you've got going on here. If the upper threads are larger than standard, you won't be able to use a standard barrel nut on it. BCM does not use nonstandard threads. |
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Quoted:
Did you contact BCM? Is it a factory built upper? No. I built this upper. It worked fine before I assembled the new barrel to the upper receiver. It allowed other KMR barrel nuts to be used (I had a barrel on it before the one in question, and it was fine). I doubt the fault is with BCM. More than likely it is my own. I have not contacted BCM. I just never had this happen before and was wondering if anyone else experienced something similar. I am not really butt hurt about it, I just figure I will keep the barrel that was on it before on this upper receiver since the barrel nut threads on with no issue. Not a big deal. |
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