by plant_one » Fri Jan 26, 2018 2:14 pm
how new is this upper and lower?
if its basically brand new heres something taht will probably help you.
take it apart and remove ALL the lube from the bcg and upper. you want it sandpaper dry. use something like bore scrubber or brake clean to get it all off.
manually cycle the action 150-200 times or so. no mag or anything. pull the bolt all the way back back and let it drop.
this will wear in the upper and mate the contact surfaces while wearing off any tooling marks. you're essentially speeding up the break in process that will happen during use and lapping everything smooth by just friction.
take it back apart, clean reallllly well, relube, and see if that helps things.
its entirely possible its a mag spring issue, but there could also be some drag somewhere else in there causing the hangups too - even if all your parts are in-spec. a rough spot of tooling chatter on the mating surfaces of the reciprocating parts of the action can cause all kinds of issues, especially those were a small amount of tension makes all the difference between success and failure.