FYI, Remington .44 Magnum brass has about 89.4% of the water capacity of a W-W .44-40 case with a 212 gr. bullet seated in both. As far as sticking chambers is concerned, have you had any similar problems with smokeless loads loaded to similar MV with the primers backing out and not reseating? I don't shoot BP, but there could be something of a low-pressure condition in some of your loads, so the cases aren't moving backward.