Just for a bit of conversation, a single shot rifle might not need crimping considerations like a magazine rifle or revolver. Maybe, watch the overall length so the forward full diameter band doesn't get into rifling or any chamber taper? I've loaded a bunch of finger seated cast bulleys for single shots, and I haven't used my lubrisizer for many years.
Just guessing if it were me, I'd request the mold to drop .367-8, and the heel to be .001-2 larger diameter than the average inner diameter of a few fired brass. I think a good fast powder would be clean burning, so I'd just decap, not automatically clean the brass, use a hand primer, drop the powder charge and push in the bullet. It will hold well enough, it's not a rattle around fall out scenario, just shoot and repeat? That brass would be reserved for that rifle only.
If I were ordering a mold, I really would not prefer to size, and I think it would still be some form of a hand lubing step. The potential is there to improve accuracy, but if it got to labor intensive, there might be a temptation to fall back to the HBWCs? I know .378 Colt revolver bullets can be purchased, but they seem a pain for the .366 groove, though there are moderately priced push through sizing dies that can be had if needed? Fun project, to me this might be a minute of three inch square bouncing target, start at twenty, twenty-five yards, and go get it when it's out too far. Happy New Year all.
