Man, you want that projectile to be tight. Your missing the point. Reason powerbelts are so easy to load is they are loose. Because they are loose, they are limited on the load you can use. Forget that.

For me the tighter the bore the better groups. Get yourself a range rod, get youself one of T/C solid rods. Work around the tightness. Its what you want.

My brother has a CVA that is the loosest bore, I ever seen. Guess what, he ain't getting no 2" groups. With any load combo.