Re: the feedway stoppage, the one I had this week with the GMM looks like the previous ones. The round gets stuck at an angle on the way into the breech. When I say "stuck", I mean it jams in there pretty solid, I had to use a chopstick point to wriggle it out.
With respect to the gun, here are the list of parts that are not as per factory.
Wilson Combat Bulletproof: Ambidextrous Safety, Slide Release (trimmed), Sear, Hammer, Disconnector, Extractor (tuned), Xtra Power FPS, Square Bottom FPS (smoothed), 17# Wilson Flat Wire Recoil Spring and Recoil Spring Guide, 19# Hammer Spring, Hammer strut, Pin, Short Trigger, Sear Spring (tuned). EGW HD High Shelf Magazine Catch, Barrel Bushing Drop-in (0.699x0.580 AB), Spring Plug Long SS Wolff Magazine Catch Spring #2 Challis Slim bushings, slotted grip screws. VZ Operator II Grips, black. Stan Chen Shooter Installed Magwell, Blue 10 8 Performance Rear Sight.
Thanks! I bought it partly to have a pin gun but also to mess around with it as I tried to learn how it worked. It's been a lot of fun, and I've really enjoyed it.