My bro shoots 20gr. in his smoothbore .60 Officer's flint pistol. The barrel on this one is a re-bored, turned & swamped 1 1/8" .58 Octagonal rifle barrel. Rather extreme work to get a barrel, but a beautiful pistol nonetheless - I'll have to post some pictures some day.
: One dueler we've seen, has the charger in the end of the loading rod. IT can't hold more than 15gr. and was for a cased set of .60's. The brass barrels at the swamp, were only .020" thick per side. I have pictures of one with 13 thousanths thick and it's brass as well. No wonder the harges were kept light. They'd have blown quickly hunting buffalo I assume.
; 30 to 35gr.3F makes a good healthy load with a 300gr. ball.