I know everyone may have different views, and im not expert by far, but first time shooting go light on the BP like around 20 grains to feel the gun's reaction. I own an original 1854 Aston Johnson .54 caliber smooth bore . It has an 8" barrel. Did research on it for loads, after a extensve inspection of the barrel and pistol itself (safety always comes first) I shoot it with 35 grains of 2F, using a .520 ball with a .010 lubed patch. I probably can go up to around .40-.45 grains but refrain cause of the age of the handgun. I have no issues at all shooting, not much of a kick either. At around 20 yards or so it hits the target pretty much spot on, not much accurate after that. But close range its spot on. I'm not a hunter, but I would make sure of it accuracy, as you want a kill shot not a wounded deer running off. Best of luck with yours. I do love mine though its not a flintlock, its fun to shoot.
Video of my son trying it for his first time. Little bit of a cringe he forgot to wear ear plugs. I'm half deaf anyway from all those 1970's rock concerts so it doesn't phase me when shooting BP firearms lololol