45/50 black Harvester sabots
44/50 green MMP sabots
Barnes Spitfire sabot/bullets
Harvester Sabertooths
Powerbelts
Buffalo sabot/bullets
Precision Dead Centers/QT sabot/bullets.... especially 40/50s
Bulk bullets like XTPs/Gold Dots in .429 and .451 with Harvesters/MMPs

Call T/C & complain. Ask them why they changed from MMP to thicker Hornady plastic sabots. Hopefully, they still have some leftover MMPs to send you.

Also... get a good T-handle for your ramrod or buy a range rod. Aways use a clean, dry bore & use lots of spit on that patch. Very lightly, lube around the plastic sabot with bore butter..... but don't put any on the bore walls.

One last thing... make sure you're using a quality solvent that removes plastic, copper & lead WITH A BORE BRUSH. I even use a bore brush for swabbing at the range. Most blackpowder solvents & stuff like Hoppes #9 are pretty weak.