This is a Polytech M1A receiver I want to rebarrel with a surplus military barrel I've got laying around, but I've never seen this before in an M1A/M14 receiver. Looks like some kind of set screw or a staked pin of some kind to hold the barrel in place (as if the torque on these babies wasn't enough already). Anyone seen this before? Do I remove it (it looks staked in place) before attempting the barrel removal?