I've never used Trail Boss, am not familiar with its burning rate. IIWY I'd look in the back of a Lyman Handbook for cast-bullet loads for the 8x57, and use the Lyman CAST-BULLET starting loads for whatever powder you have in stock. You shouldn't need more than maybe 2 dozen in total, just be sure to clean the bore thoroughly after each successive grit size change.

Hope it helps but frankly IMO it'll probably need something besides fire-lapping. F/L works quite well on new barrels however.
Regards, Joe

You can lead a man to logic but you can't make him think. NRA Life since 1976. God bless America!