I have used then a couple times with in-consistant results. But as BP steel is "softer" one generally has better results.
Have you looked into "PLUMBROWN" finish? Its not blue but brown and applied with heat. I think its wonderful for muzzleloaders and adds a nice "patina" look to them. I have done a couple Marlin rifles with it as well as a muzzleloader barrel, all came out really well.
The stuff I used was made by Birchwood Casey.
Good luck,
CW
