I've been cutting 1/8" thick wads for my .50-caliber, Hawken-pattern rifle for years, using the same felt I use for my cap and ball revolvers. A 1/2-inch hole cutter does the trick.
I used to lubricate these wads with Crisco or CVA Grease Patch, but began using Gatofeo No. 1 lubricant about 10 years ago. The difference was apparent: less fouling, cleaner bore, no need to run a cleaning patch down the bore every few shots.
The felt wad, greased with Gatofeo No. 1 lubricant, is seated firmly on top of the powder charge, followed by a .490 ball enclosed in a patch also lubricated with Gatofeo No. 1 lubricant.
I use Gatofeo No. 1 lubricant for all black powder applications: felt wads in rifles and revolvers, felt wads in shotguns, patches and soft lead bullets used with black powder. It's too stiff to be used as grease for moving parts, or on a cylinder pin. For those I use CVA Grease Patch (I believe now discontinued) or a mix of olive oil and beeswax.
Incidentally, I never named the lubricant after myself. Shortly after I began posting it, singing its praises, people began calling it the Gatofeo No. 1 lubricant.
I much prefer using felt -- and real wool felt, such as that sold by Durofelt on the internet -- over any other material. Felt will hold a fair amount of lubricant, leather will not.
When it comes to black powder, I'm a firm believer in having plenty of it to keep fouling soft and moving parts slick.