What barrel finish is historically correct for a Colonial-era longrifle?
Bluing is typically not recommended because uneven heat can cause the barrel to warp. If you're after historical correctness, the only bluing that seems plausible for the colonial period is charcoal bluing, and even that carries warping risk unless done carefully. Browning came in the last decade of the 18th century. Anything prior to that would be polished bright, charcoal blued, or simulating some sort of age.