And I've been working with Doug Turnbull for most of two decades. His turn-around has always been excellent, you can talk with him about how hard you want it and he varies the colors to what is appropriate to the type of gun. Doug has more experience bone charcoal case hardening than anyone else in the country.
Doug also offers the best commercial charcoal bluing I'm aware of.

All mentioned would be good folks to do business with.
I'm also sorry to hear about Don, he's done some great coloring for me as well.