Thanks--it's actually a very simple set-up--my first stab at a blow-back build, and I'm very partial to 10mm since I've had a glock 20 for quite some time (though it spends much time in the guise of a 9 x 25 dillon now). Speaking of PTR's
the ejector hook which the bolt rides on reminds me a heck of a lot of the one on a PTR functionally. The downfall of this particular design, IMO, is the pin/rod which tries to do too many things--engages the magazine, holds the bolt catch etc. and if it's slightly out of tune the whole cycling system can easily be thrown out of whack. If I did one of these again (and probably won't, unless maybe a 9 x 25 dillon) I would get a lower that didn't enslave you to glock magazines only.