That is a bit surprising about the powerbelts. Have never shot them but know many who have & all got good accuracy. Of course most are with fast twist barrrels.

Seems that the 300-grainers should be more inclined to keyhole than the 250's, since longer bullets generally require more stabilization. I guess since the sabots are the same length that wouldn't matter though. So many things are counter-intuitive with these black powder rifles. I'm sure there's always a physics-based reason for what happens but sometimes it would probably take some mighty sophisticated equipment & testing logic to find it. More fun to just shoot it a bunch & let the targets decide what works