This is the first year I've used my mossberg 535 for waterfowl because I've had the gun for less than a year. Anyway I'm having trouble with rounds firing and I know mossbergs usually shoot no matter how dirty there are. With that said I've cleaned the gun and I'm still having problems. The shells even have dented primers and I've changed ammo to see if that was the problem. Anyone have any ideas? Spring? Firing Pin?