Dirty chamber? Burr in the chamber? Overpressure rounds from too much crimp or untrimmed cases?
I would first start with the chamber by pulling the bolt and then use a chamber brush or a bore brush the size of the case. Lots of solvent, and maybe even chuck the brush up into a cordless drill/driver. Followed with a mop of suitable size and polish it a bit.
Any real cartridge isues I'll let somebody else with more reloading experience investigate. That's about all I can think of.
What exactally did you use to clean/polish the chamber? How did you do it?UPDATE !! I cleaned/polished the chamber as many have suggested above..Shot gun yesterday and the empties JUMP out of the chamber...did a nice, well neeeded cleaning while bolt was out....Thanks everyone!! John