I recently put together a rifle from some spare parts I had lying around and parts I picked up on the EE.  (Colt upper, colt barrel, colt BCG, Spike lowers, colt LPK, Colt Buffer).    I am having issues with it feeding rounds out of PMAGs.   Mainly Gen 3 Pmags.  It is also very difficult to seat a loaded mag (PMAG or USGI) when the bolt is closed.  When I go to close the bolt it sticks about halfway open, partially picking up  a round.   Any idea what could be causing this?  Thanks in advance.

Frank

Needs lube and break-in.

Ill go put some more rounds down range and see if it continues.  (Only about 150 so far).  Its properly lubed up though.   Thanks

Only real issue that would cause feed issues are the buffer/spring combo and the feed lips on the barrel extensions.  That's a rare one though.

My buddies ar was double feeding this passed weekend on the range.  His buffer was to heavy.  Causing short cycle.  

Your mags is just a break in problem.  I had the same problem with my gen 3s.  I slapped them in empty, made sure the bolt was lubed, and repeatally ran the charging handle about 85% without locking the bolt back.

It helped but you won't get a nice postive mag lock until you get in range time.

I personally think a combination of the heat, pressure, and gas is what really gets the plastic formed and broke in.