Actually, I'm having the opposite problem with regard to the shimming. Them mag actually binds up left to right, the outer casing is bowed a bit in the center. It's got movement in the up-down, forward-back directions, I actually had to remove the shims I had in the magwell for my short mag. I did "rebuild" the mag catch with JB-weld, and I left it a deal larger than normal, but this worked perfectly with my short mag, this may need to be re-modified.
2 more questions I have:
You have what I assume to be the King Arms upgrade nozzle. I have the stock nozzle and hop(stuck with it, its breakdown), and I notice that yours juts out around 3/4ths of a centimeter, whereas my stock one is recessed about a quarter of a centimeter. Would moving that forward substantially improve the air-seal, or is this mainly needed with the nonstandard hop/nozzle sets.
Also, on the slide checks, do the male ends have some kind of pressure hold on them? On air compressor fittings they do not have a way of holding in the pressure on their end of the line, and I'm trying to figure out a good way of keeping a seal in the mag so I can still use the gas port if I run out of CO2 caplets or something.
Edit: have another strange problem with the new mag, it's expending a much greater amount of gas than is needed. The first 3 shots come out extremely hot, and then it's extremely underpowered, didn't have this problem with the standard mag. I'm not sure if the striker is holding too long or what, at the moment, but could this be a problem with the mag sitting to far back?