I've had my 870 do similiar things with diferent sized shells..you are correct..Mine has never totally locked up { Been hunting for 45 years }...I forget now but one of the shells did not eject smoothly for me neither..it might have been the 3 1/2 Nitros ..I use 2 3/4 " Winchester slugs..fact I'm using it tomorrow..I shoot them out of my Improved Cylinder choke and it consistently puts them in the money at 100 yds..I'm actually flabbergasted..My Ithica ..went back into the gun bag..forever ..The 870 Mag. Remington is unbeleivable.The Gobble Dot site helped a ton though..it did not shoot like this out of the store..I had to shoot it in.