For nearly every long rifle there are some old tried and true traditional rules of thumb. slow twist is for round balls, for guns under 50 cal use fffg, for guns over that use ffg. For starting loads use the same grains of black powder as the bore size, ie 45 caliber, 45 grains, and a max should be twice that, ie 90 grains. The best hunting load is usually around 1.5 times the bore size, ie 67.5 grains for a 45 cal and 75 grains for a 50 cal, etc. You can use a coarser powder in the smaller bore but not finer powder in a large bore.
With modern steel and components, some folks feel the need to always push the envelope. But these "rules" have been in existence for 150 years or more. Don't get carried away by the Popeye Complex, that if a little is good, more must be better. Folks will post downright idiotic things like, "I use 8 90 grain pellets of super poop powder and never blowed my head off." Your gun is a good serviceable firearm, but made with mild steel and was never intended to withstand "three stooges' loads".
