Rufous, remove the bolt and clean the bejeezus out of it inside and out, Bolt as well as the receiver ect. If that doesn't take care of the misfires have the headspace checked and replace the hammer spring. As far as the tumbling is concerned I would guess that you have a heavy lead buildup in the throat from trying to push the plain base bullets too fast. It is essentially sizing them down when firing and then little if any rifling engagement. Clean the bbl. with copper "chore girl" cleaning pad material wrapped around a brush dipped in Hoppes by scrubbing the hell out of it. The copper must fit tightly and after 50 or so strokes run a patch through it and there should be lead slivers on the patch. Keep going till the patches are clean. To test run a tight fitting patch through the bbl. before cleaning and you will feel the patch catching on the lead. All above is just a guess but is where I would start. Good luck keep us posted-Muddy
