T/C's like a fairly tight bullet/sabot combo.
I'm thinking you're right BirchOrr
The reason I can't get the very easy loading PowerBelts to fly very well out of my TC.
Haven't tried to do it but if I were going to cast conicals for my TC, I'd probably cast an all lead, well lubed oversized projectile.
Course, there are a few that have posted here on TFL that their TC's shoot PowerBelts and other full size conicals well. Again, gotta figure out what each rifle likes, eh.