Actually as a historical fact there were a very few muti-shot muskets that to the best I can figure must have operated on a roman candle type effect... Probably a side barrel with powder to burn from one to the next but its just my guess..
All that aside you can simply look up what the founding fathers said about arms and the government... Really quickly they realized the government could easily be a threat to the people and that the people would need arms appropriate to combating a over reaching government....
So basically anything appropriate for military action short of weapons of mass destruction is IMHO a allowed arm under the 2A. (Im not advocating breaking laws). Further (and no one ever, ever learns apparently) as a historical note time and time again when governments are the only ones with arms at some point or another it goes really badly for the people..