When I started shooting black powder in 1976 it was recommended I use Crisco grease as a patch lube, so I did. I used it for both hunting and target shooting for 10+ years. It was an accurate lube for hunting though very dirty, as long as I would only shoot 3 shots then clean the barrel with spit patches before shooting the next 2 I could maintain that accuracy. By accurate I mean I won a lot of matches including a 3rd place in the 50 yard offhand at the SE Regionals one year.
When hunting I always left my rifle loaded until I got a shot. Then a thorough cleaning and reload.
During all this time in a very humid environment I never got any rust at all in the bore. Several times I have considered going back to it for hunting.
And no for you California desert boys, my Crisco never caught on fire.