I shot cap and balls for years. I started out putting Crisco
in the chamber because that was the advice I received
as a novice. But, apart from it being messy I figured
that it was more likely a chain fire would be caused by
a bad fitting cap than a spark passing by a tight fitting ball,
and going backwards to boot.
Plus, back when these revolvers were in vogue and were
carried on the hip, then if indeed the guys used grease, then
in the summer months their pant legs must have been
covered in grease stains.
I never had a chain fire either with or without Crisco.