Pistol primers and BP? Range time! Load testing with various primers led me to that conclusion rather than follow Garbe and Venturino's red herrings (magnum primers and over primer wads). I put 350# of lead and nearly 40# of BP through one Shiloh Sharps in one year.
I never liked SPG as it would melt if cartridges were subject to a warm day. Too, I had tried other lubes and thought that they kept fouling softer. Lee Shaver's BP moly lube was good stuff if you pan lubed with it, but like SPG, it would "bleed" oil in the lubrisizer.
Good BP lube can be made with beeswax as the base carrier, anhydrous lanolin, and any of a variety of oils. More lanolin than fiver and Ian are mentioning can and does work. One recipe that comes to mind is in proportions by weight, 7-3-3. Beeswax, anhydrous lanolin, and Dexron III ATF or Mobil 1 full synthetic 15W-40. Both of these work very well, but the ATF version will hold more moisture in the barrel (blowtube) to the point that it can be too much on very humid days.
While I don't have that previously mentioned Tom Ballard PP mould, I had one cut to emulate the military .43 Mauser bullet. I disassembled an 1885 vintage military cartridge and got my dimensions there. The .43s had very deep rifling, and the naked bullet was just over bore diameter, and patched to just under groove diameter. The resultant PP was expected to be loaded into a fouled bore, and the rifling guaranteed to slice through the PP. I've also PPed 45cal pistol bullets and shot them over smokeless in a Marlin 45-70. Somewhere here in my mess is a couple of boxes of Winchester PP bullets, 40cal, I think.