The last site I was on suggested that a really good soldier could manage 6 rounds a minute, which is essentially a shot shot per round. Average was closer to three, so every other round. I might even go to a two round reload if I were making the weapon list from scratch, but add in abilities by level to cut that down. In all those cases accuracy was mostly junk past about 100 yards (a very loose and general number). So maybe something like 100/300 with a -3 to hit at long range. Again, abilities could cut that at higher levels.
I'd rather an adventurer have a musket and a brace of pistols than have to faff about trying to make people happy with starting reload times for the long gun.
I got a colleague who did the exercise with historical weapons and he estimated that you could manage do load a musket within 10-15 seconds