Way back in 60's an uncle had an M1 carbine converted to M2 (leagally via Class 111) I think real cheap then. He passed and my cousin found this long forgotten thing (unc was sick a looong time) got all the paperwork done but it won't work. He came to me 'cause I'm sorta the family 'gun guy', tho I don't know much on autos. On semi auto this thing works great, when you flick that switch to auto, it don't! It will fire, eject; reload and the hammer will fall but not fire. With a magnifying glass you can barely see a tiny mark in center of primer. Do these things have to be timed? We dry worked it without stock to watch parts and everything seems to work. The lever levs, discon. goes down; sear releases and hammer falls, this all "seems" to work after the bolt is closed during that final bit of travel of the slide, 'course this is dry working, no round is fed or seated. Could the recoil spring be just weak enough that the action slows enough when going 'hot' that the hammer falls before it fits in the groove to hit the firing pin? I'm stumped on auto stuff, it looks like everything does what it should but it ain't goin' bang.