Oahu, try paper patching a bullet that is .004-.006 below bore/rifling diameter. Get the package .001"-.002" above bore/rifling diameter. That at least gets the bore filled and the projectile gripping the bore. I use lead in the range of BH 7-9, which involves the unscientific method of melting chunks of sheet lead and adding wheel weights for tin to get the complete fill of the mold. I now use a lead hardness tester, which confirmed as OK my past hillbilly approach to pouring lead projectiles.
These guns were made to shoot paper patched bullets. Black powder can "bump up" the heel, but I've learned that more than anything youve got to fill the bore.