why do you need one ?????????????
if the rifling looks bad, it may be because of leading !!!!!
i have bought a few .357 M. Blackhawks, & the barrels were badly leaded, so i plug one end of the barrel & fill it wyth mercury & let it set for a few hours, pour the mercury back into a container, run a wire brush thru the barrel & it will be as shiny new as the day it left the factory, take it to a gun show & double or triple my money, simply because some fool thot his barrel was shot out.........