Re: "gun" used to mean a non-portable projectile weapon
Sorry, but you are way wrong about there only being single shot firearms during the American Revolution, much less when the Constitution was written.
The Continental Congress gave a contract to John Cookson for 100 of his lever action repeating rifles based on the Lorenzoni system, which was developed in 1660. Cookson also offered his gun for general sale in Boston Globe advertisements.
If you are in England,an example of the Cookson repeater can be seen in the Victoria and Albert Museum, British Galleries, Room 56, The Djanogly Gallery, Case 5.
There were also Cookson model repeater handguns, Loernzoni handguns, and eight shot revolvers-yes I said revolvers.
If you find yourself in Lillehammer, Norway, go to the Maihaugen Museum and ask to see the revolver used by Georg Von Reichwein during the Thirty Years War. Hans Stoppler was the gunsmith and made the revolver in 1636.
There are many examples of multiple fire repeating firearms during the 1600 to 1800 era.