First of all, BIG thanks to rahatlakhoom for doing the welding I couldn't do with my buddy's 90 amp mig. Also thanks goes to anyone else who has built one (I did a LOT of research).
This is my 3rd gun (also have a Saiga 223 and a Remington 11-48 12ga) and my first build. I come from a hobbyist machining background, that experience made this build a lot easier than it would have been. I started with a AMD-65 barrelless kit and a PPsh 16" barrel. I'll list the highlights that set it apart from others.
-The receiver was shortened nearly an inch and a quarter.
-The top cover is hinged at the rear sight block so the rear sight can maintain a zero.
-The front sight was welded to the gas block at 3/8" over the standard height to align with the HK rear.
-The barrel had to be sleeved in 3 places to fit the trunnion, hg retainer and FSB.
-Mag catches were welded to PPs-43 magazines to fit in an aluminum internal magwell.
It was running at about 85% efficiency with S&B ammo. But now I got a case of polish surplus and the firing pin isn't puncturing the hard primers. I reworked it a bit and it should be working better now.
The main problem I've been having is that sometimes it will short stroke, not resetting the hammer (NOT hammer follow) or ejecting the cartridge. Its quite puzzling since when it works, it has a nice crisp kick. When it short strokes, the kick is very weak. I think more polishing and filing of the rails would fix the short stroking.