Sand blasting was a big deal for builders about thirty five years ago. Besides everybody trying to get that old timey look, many were trying to make the barrel less reflective. As is always the case it got taken to extremes.
I am currently helping another shooter/collector rescue a very nice longrifle that got the sandblasting treatment not only on the barrel, but the lockplate as well. These parts look like they were dug out of the ground. The cold browning solution that was used was pretty aggressive to start with, and applying it to etched metal made almost impossible to stop.
I urge caution using this technique, it can get out of hand pretty easily.
The dark textured browning so often seen on modern muzzleloaders is most likely not what the new gun had on it. Old browning recipes often call the color “plum brown”, or a clear reddish brown, the dark chocolate color seen today is likely modern builders duplicating what they see on antiques today, after a hundred and fifty years of no oil, in a closet, or attic.
Hungry Horse