I take some of the parts out of the gun except the bolt, I am not sure if all the 膠碎 is in the bolt, i only find 2 膠碎 in the gun, for the Folding stock 個制, mine is not so firm, but not so easy to press it, so that is ok for me.
The problem I faced is that I need to use 暴力 to insert the pins back to the gun when I change the 2 round burst handle.