Best guess would be that the round didn't have enough recoil to properly cycle the gun. Were you limp wristing it or anything like that? What rounds were you shooting? The new ones need a bit of time to break in properly to. Mine got alot smoother after feeding a few hundred rounds through it. I'm probably at the 1000 round mark, and I've only had it 2 1/2 weeks so I'm no expert. But you may want to try out different ammo too.