I'm wondering if the JSG powder had anything to do with that. Have you used JSG in it before?
Me thinks the only powder it has used is Goex Pinnacle. i know that it has never been loaded with Pyrodex or 777. Now that Pinnacle is no longer being made, i have to stock up on 2F and 3F JSG.
The musket cap nipple i used is not the TC Flame Thrower nipple. The
Flame Thrower nipple has three flash holes and it allows too much blowback. Much of the crud problem problem with the Black Diamond is because of those Flame Thrower nipples.