"Has anyone ever tried paper patching conicals, like in BPCR, in a muzzleloader? Would there be any advantage to it instead of a properly lubed bore sized bullet?"
Keith, I tried this once with a Lee .50 cal. 320 gr. REAL bullet because it was too small for the bore of my Knight Bighorn. Needless to say accuracy was poor. Paper patching improved the fit and accuracy, but it was hardly a tack driver at 50 yds. Paper patching can be used to maximize accuracy and allows you to push pure lead bullets to a higher velocity without leading your bore. Such bullets, as opposed to those cast of wheel weights and 1% tin, will reliably expand, making them very useful for hunting. However, paper patching takes a bit of time to master and adds another step to casting.