A couple years ago, I made an aborted effort at writing up some historically reasonable firearms rules for D&D. (It wasn't pretty, as it kinda used mixed rules from 2nd and 3rd Ed.)
I saw someone add that a skilled ACW Musketman could put off 10 rounds in a minute. A round every six seconds, I'm presuming they're referring to a muzzle loaded Springfield 1861/63 or 1853 Enfield, as those were the most commonly used firearms. The reality is, plainly, no. 3 rounds a minute is what was expected, and it's going to foul up on you bloody quick.
Lastly, on Mount and Musket: I'm not really impressed by it, but... since Battle Grounds 2 isn't really played anymore, I guess people have to get their musket fix in somehow.