Oly,
Yes, I use a card under my bullet. I only shoot Goex. I load black for my .45 LC and for my Trapdoor. If you load the full 40 grains that the original .45 Colt used, you will be in for an awakening. That is a hell of a load. It will have to be compressed also, I made compression dies that work for both the .45 and the .45-70.
More to the point. I use both flat base and hollow base bullets. I only use flat base in the .45, always with a card; in the -70, I use both the flat base 500 grain Govt bullet, and the hollow base 405 gr Govt bullet. Always use a card under the flat base. Do not use anything under the hollow base bullet. There is a reason it is hollow and that is to get it to expand to fill the grooves. If you use a card or grease or anything else under it, you just make a flat base out of it. Then it is going to lead the barrel. Remember, that on the BP loads, you are running low pressure, often not much more than 15,000, so your bullets have to be cast soft, not more than 20-1, and if that is not accurate try 30 or 40-1. If you get them soft enough, they will settle down because they have to obiturate to fill the rifling. Hope that gives you what you need.