I've been having similar issue with a less that 1000 rounds fired shadow. My bullets seem to be nosing down either jamming on the magazine itself (projectile side) or the bottom of the feed ramp. this just started happening the last 300 rounds and i've put about 300 through it previously flawlessly. I am shooting reloads so maybe i will check the length on them could like an easy fix if thats it (it is possible that there are two different batches mixed in there). It has been doing it with two newer mags and two older mags so I'm going to rule out that (started with the newer mags then the older mags started jamming in the same day). I also have three brand new mech-gars that i haven't used yet so i will try them also with the suspect ammo.