ORIGINAL: cayugad
You can fire lapp them as well, but be careful. Just apply valve grinding compound to REAL Conicals and shoot them off with moderate charges. After ten shots, clean the barrel and check the amount of barrel that has been removed. I have never done this, but heard of others doing it...
FWIW,
There was a write up on both the materials, procedure and results a while back in Muzzleloader magazine (ca 1992-4). IIRC they put 10 shots with 3 grits through and managed to salvage what was basically a shot out-rusted out bore after they were done. Believe that they used something a bit finer than just valve compound...
Myself, Im real reluctant to go through either lapping exersize unless the bores get REAL bad as seen with a bore scope. As yet neither my TC (vintage 1976) or my home built (36" Green Mt 1:70 twist) are that bad... even after having sent roughly 3000 rounds of Goex 2f through the pair of them...
Keep yer powder dry,
D.