I understand you can use full diameter lead Powerbelt bullets with a attached plastic skirt. Could you also use a different brand, full diameter, all lead bullet without a skirt, but with a polymer tip on the nose? Please see the following website.
Under existing Fish and Game rules for hunting with muzzleloaders during a muzzleloader-only season, polymer tipped projectiles are considered illegal. The plastic skirt on PowerBelt bullets is considered a gas-check, much like the cloth patch used with roundballs, and is not considered part of the bullet. Polymer tipped projectiles, along with jacketed muzzleloader bullets, can be used during any-weapon seasons.