They’re individual weapons
Letters of Marque then, which probably referred mostly to ships, were armed with crew served weapons, which at that time and for a while after were cannon.
If they intended only for firearms, they would have written that into the Second. But they didn’t, and they preferred us to have “every terrible weapon” of war. Thus, they wrote ‘arms’.
I have to respectfully disagree. One way to tell is to read the Federalist Papers as well as the Anti-Federalist Papers and the personal documents of the Founding Fathers. Since I teach AP Government, I make it a habit to make my students read all of those and do a written analysis. In a great many of the papers and letters written by the Founders in those times they mention the rifle and sidearm. George Washington himself owned over 50 high quality rifles. Nowhere are the other implements mentioned. Also, I think the term arms would be limited to what an individual infantryman would carry and that one man only. Thus crew served weapons are probably again covered under the letters of marque.
So if it requires more than one person to operate I don't think it falls under the infantryman's TO&E. However an M60 or a SAW can be handled by one man. I know, I've done it. I can set up and fire a Ma Deuce by myself but I can't hump it on my back alone.
Every terrible weapon of war? It is assertions like this that are going to cost us the right totally! Things like that happen when you open your mouth and shoot yourself in the foot .. on full automatic. I'm not trying to be rude here and I apologize in advance if it seems that way, but we have all heard a fellow conservative utter a damning phrase that we just KNOW is going to be misquoted or stretched out of shape by the liberals and that is going to be our undoing. I'm probably guilty of the exact same thing earlier in this thread when I told somebody I favored mounting fore and aft machineguns on cars in NYC. So I'm not immune.