When I size and lube my cast bullets I use the same lube (SPG) no matter if they will be powered by black powder or smokeless. Sometimes black powder bullets get lubed with Dick's Pearl lube if I feel like cleaning out my sizer of SPG. If I'm going to reload milder loads in my .357 Mag, 44 Special, or 44 Mag revolvers, a few times I've used the same softer lead bullets I use for reloading my conversion black powder guns (38 Spec and 44 Colt), but generally I use a harder cast bullet on the 357 and 44's, some with gas checks. Never a problem using the same lube for smokeless or blackpowder.