mine was doing that too, i as well was using the same rounds....i was blaming the rounds, as i do clean the gun, then ran into a guy that told me to use a wire, knife or whatever to scrape the carbon buildup where the shells rim seats in the barrel. i did this, didn't seem like i cleaned anything, but....the gun now functions fine. i guess the round just wasn't fully seating, if that's the right terminology.