Check out Quackbush air rifles, made in Missouri.
Not exactly a muzzle loader, but fires a .495 round ball...
For Big Game, Elk and Black Bear up here in the mountains of centra-western Idaho, I use a CT Arms, Hawkin .54 caliber with about 120 grain load. good little recoil, but it does take them down. Please forgive my spelling.
The Brits were so put out by this they declared these rifles as unfair and ungentlemanly and that they should be banned
Their thought was that by deliberately aiming at officers, the rifleman was committing murder as opposed to pointing one’s musket at an enemy formation—the ball might or might not strike someone. Their army’s method of fighting (and it was quite successful world-wide) was to put more lead in the air, faster than anyone else. For that the Brown Bess was very good.
It wasn’t until our army could fight the British way successfully that we started to win the big battles. Although riflemen/snipers at Saratoga did take out quite a few of their officers at long range.
Ha, interesting. American innovation. Better guns, better ships. And they didn’t just stand out in the open when under fire.