Looking good SL! A nice find for sure. MK's are just great rifles, I've never had one that wouldn't shoot if I did my part.

I use Pyrodex in my plunger guns, and have never had an issue. I like it, and it cleans easily with most cleaners, or soap and water. I'll admit, I don't do the soap and water thing much anymore either...but have never had an issue with it. I do use it on sidelocks.