smokeless in my 1873 original is just fine if you keep the pressure down, around 1200fps ,
i use trailboss its a very forgiving powder for all "cowboy"loads and there is no chance of a double load its so bulky, its not temp sensative so no filler (dacron or the like) is needed.
just remember these smokepoles are 120+ year old and common sense should prevail when loading smokeless but keep them mild and they are great fun.
BP is more funner though.
casting my own i use ideal molds 457124---405grn and 457125---500grn,
i have the 457130 coller button it drops around 145grn ,,this is gonna be my "catsneeze" plinker ,i haven't shot it yet but i'll bet its fun.
be sensible and shoot safe and have a great weekend.