There have been problems with the cocking tube gap (too small) on many pistols. This can be fixed with adjusting the length of the inner cocking tube. The rear pin (inside) spacer for the stock pin should have another weld to the receiver. It is said that just using the end cap makes this worse. I can see that the recoil is directed into the pin, not into your shoulder when there is no stock. The is another member here who replaced the Locking Piece with a different number and it ran smoother.
The 40 round mags are sloppy in the mag well. This might cause alinement/feeding issues or the bolt carrier slapping the mag out of the mag catch.
I like mine. It wouldn't run two rounds consecutively till I changed the LP with an RCM #15. Since then it's been perfect. The end cap had to be hammered off it was so tight. I made then pinned and welded a barrel extension and then installed an mp5 stock which fits great. Snug but can be un-installed without a sledge. Cocking tube indexing doesn't seem to be a huge deal to me since one wouldn't be aiming an empty gun anyway. I do agree that 40rd mags rattle around a lot but i've never had a problem feeding from them.
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