I'm not sure how much I can contribute to this discussion, but, FWIW, the use of the rifle, as a military weapon, was quite well-know, and certainly by the end of the American Revolution. Admittedly the musket was still the general weapon of the infantry, but Daniel Morgan, who eventually rose to the rank of Brigadier in the Continental Army initially commanded a unit composed entirely of riflemen. Other Colonial/Continental forces had rifle units attached to them. They did not stand in massed ranks for the exchange of volleys. However, one of their principle tasks was to remove British officers from the field, which they did with varying degrees of success. One of their most notable achievements being the removal of one of Burgoyne's generals during the Battle of Saratoga. Mel Gibson's movie "The Patriot" has Lord Cornwallis making an explicit reference to the removal of British officers by the Colonial/Continental forces during combat. Given this, it would seem possible that the song could still be traditional, even though refering to a "rifle".

Just a thought.

Robby