I am not Rick of course, but...
It would be "FFF" ( "FFFF" was and is reserved for use in the Flash Pans of Flintlock Arms, or, maybe some kinds or elements of Fireworks ).
Present Day 'Swiss' Powder, in it's 3F equivalent Granule designation, would be the optimum choice and likely closest to what was used then.
"SARCO' I think? Sells a 230 Grain, 453-ish Wadcutter ( flat bottom, raised circular 'nub' on top, and, they can be loaded Backwards for a full flat front Wadcutter effect ) which might be just delightful in any old .450/.455 and their likes...one could bump it out a little using a .455 Bullet Sizing Die, on an Anvil, with a co-responding counter-Bored Flat Nose Punch ( one could make out of anything ), to have a .455-ish version.
Some other Companys offer 454-ish DE Wadcutters also, but I can never remember who they are...maybe someone else knows?
I Love Wadcutters in 45 Calibre...( as my Avitar may suggest! )