I'm thinking that the bolt and carrier are too light. If anything I've reduced 10-20% of the bolt carrier's mass and SMG's have heavy bolts. I'm going to replace the piston with a solid steel rod to fill up the gas tube to try and add a few ounces.
Also I need to replace the feed ramp with a steel one slightly lower than the current aluminum one. The second magazine I modified is slightly loose and too low and misfeeds more often than the first one I made.
The third problem: the charging handle broke off... again. Trying to operate this gun when dirty without a charging handle and with the bad magazine is one of the most frustrating gun related experiences I can think of. Every other shot I had to undo the top cover, remove the magazine, clear the jam, pull the bolt carrier back, insert the magazine, let go of the carrier and close the top cover. The problem is that welding on the funky alloy the bolt carrier is made of is very very hard. I'm planning on making a new charging handle and either bolting it in or pressing and staking it in to avoid it ever breaking off again.