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12/14/2008 5:20:39 PM EDT
I just put together an AR-15 9mm pistol.
It fails to fire 9 out of 10 times... not even a mark on the primer.
I swapped trigger group, and the complete bolt... still.

could it be the upper?

any ideas?

Thanks,
H.

12/14/2008 8:08:27 PM EDT
[#1]
Hammer spring installed the right way?

Bolt fully closing on the round, or is the mag well block ejector catching/binding on the bottom of the bolt and preventing the bolt from going all the way forward.
Note: you want the ejector to just kiss the bottom of the bolt.  To much gap and the ejector will not knock the spent case off the bolt face.
12/17/2008 3:47:07 AM EDT
[#2]
I got it figured out yesterday... the barrel was not all the way back! I did torque it to 50 Ft. Lbs. but it looks like it was stuck an eights of an inch too far. I compared it to another upper, and it was obvious. I removed the handguard (YHM) and put it back and that worked.
I will take it to the range and see how it runs sometime this week.

As a separate question, what can happen if someone excessively over torques a barrel nut?

Thanks,
H.
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