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9/11/2013 4:22:34 PM EDT
When I go to the range I shoot both .22lr and .556 out of my carbine. If I shoot .22lr first then transfer over to .556, I normally encounter drag (friction) inside the upper receiver, which slows down the bolt carrier group and sometimes prevents from going into battery. I understand that .22lr is dirty and without cleaning before switching over to my .556 bcg, this kind of drag can be expected.

This process brought a question to mind. What would happen if the internal diameter of the upper receiver was opened up by the smallest degree to loosen the tolerances a bit? I understand that this is a well designed rifle and the internal diameter is meant to be well matched with the BCG but this idea still has me wondering if anyone has done this before with any success/ failure.

Thanks,
Nate
9/11/2013 6:23:14 PM EDT
[#1]
Get a 12 gauge barrel swab.  Use it to scrub out the upper real quick and wipe it down.

Get a bore snake and pull it through a couple of times... and lube.

A much better idea then machining through the anodizing.
9/13/2013 10:06:55 AM EDT
[#2]
Call it general principal, but that does not seem like a well thought out plan.
The anodizing is a hard coat that protects the aluminum from wear and corrosion.
9/13/2013 7:34:06 PM EDT
[#3]
Quoted:
This process brought a question to mind. What would happen if the internal diameter of the upper receiver was opened up by the smallest degree to loosen the tolerances a bit? I understand that this is a well designed rifle and the internal diameter is meant to be well matched with the BCG but this idea still has me wondering if anyone has done this before with any success/ failure.
View Quote


What will happen is that the carrier would rattle around more as it went back and forth, instead of sliding in a mostly-straight line.  The amount of rattling would depend on just how much you opened up the interior of the upper.

A rattling steel carrier would quickly damage and abrade away the interior of the aluminum upper, and you'd probably render it functionally inoperable due to that damage within a few thousand rounds fired.
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