If they didn't tell you what the lube was, I would assume that it's a smokeless lube. In addition to the lube, bullets made specifically for blackpowder are usually made of soft alloy (20:1 or 30:1 lead to tin, or thereabouts). So what I'm saying is that a BP bullet will be softer than normal and have a special lube - and if that was the case, you would think the seller would mention it.
If you want to stick with one lube for both BP and smokeless, then it should be a BP lube. BP lubes will work fine with smokeless, as long as the MV is not too high. I would say you can use most BP lubes up to a MV of 1800-2000 fps (? - comments welcome on this. I have never shot a cast lead bullet with BP lubes this fast). So if you're using the smokeless to duplicate BP loads, and the MV is in the 1100-1400 fps range, a BP lube will work fine.
There are lots of BP lubes, and dozens of recipes for home-made. SPG was one of the original commercial BP lubes, and it works great.
Here are 2 simple homemade formulae: 50/50 beeswax and olive oil (use the cheap grade of olive oil. I would think that any other vegetable oil should work fine also).
My favorite is 50% beeswax, 40% Crisco (the solid, white stuff in a can), and 10% vegetable oil. This is know as "Emmerts" formula.