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2/17/2012 9:30:05 AM EDT
When I am reassembling my Colt M4-style AR-15, the final step is to rotate the upper and lower around the pivot pin, and then engage the takedown pin.  Sometimes, the firing pin slides backward a little and the hammer hits the rear edge of the firing pin and prevents the upper from properly mating with the lower.  In order to fix this, all I have to do is push the firing pin in a little, and the hammer slides up behind it.  Is this normal?
2/17/2012 9:33:52 AM EDT
[#1]
You should cock the hammer before closing the receiver, this will solve the problem

And yes, it is normal


2/17/2012 9:34:09 AM EDT
[#2]
Quoted:
When I am reassembling my Colt M4-style AR-15, the final step is to rotate the upper and lower around the pivot pin, and then engage the takedown pin.  Sometimes, the firing pin slides backward a little and the hammer hits the rear edge of the firing pin and prevents the upper from properly mating with the lower.  In order to fix this, all I have to do is push the firing pin in a little, and the hammer slides up behind it.  Is this normal?

Push the hammer down in the fire position and it will eliminate the problem.
make sure bolt is extended in bolt carrier when sliding into upper receiver
make sure carrier and bolt are fully seated into feed ramp.

2/17/2012 9:34:13 AM EDT
[#3]
You're reassembling with the hammer forward?  Why?



Set the hammer and put the rifle on safe, no more interference.


 
2/17/2012 10:31:03 AM EDT
[#4]
Normal. Either cock hammer or check firing pin before closing. I usually close it on a de-cocked hammer as well(I'm probably not using it when I'm working on it, so I don't see the point in cocking it) and I just check the pin or give it a little rap while it's nose down to ensure the pin is forward.
my .02
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