In my MR-X .45, I have tried Hornady .40 200gr SST with mmp? sabot, .40 arrowhead with blue harvester, both fury .45 sized to .453 all start out tight but around 12 inches the bore opens up and only takes few pounds pressure to push rest of way. The .45 powderbelts do the same thing except easy pressure from the muzzle.
I only took out once after sight in at 67 yards, 75 grains by weight blackhorn 209, winchester 209 primers can fire different bullets and all will touch at that distance. Need to narrow down a load at further distance. Still concerned with bullet movement while hunting (if i can ever get out).