Yes, I have a time or two seen signs and symbols of our Craft on original rifles at the Kentucky Rifle Association annual meeting in Carlisle,Pennsylvania.It's unusual,though. One that stands out,though not a rifle, was an American double barrel fowling piece made in New York in 1810 with a square and compass on the trigger guard. It is more common,as you mentioned,to see symbolism on horns,but look other places also.
Remember,though,that Freemasonry wasn't very active in the Colonies until the F&I War when British regiments were posted to the Colonies.It was after 1763,really,before the Craft got much of a foothold even though Freemasonry had been active in England,Wales and especially Scotland since the very early 1300's and even earlier. Scan Neumann's and Neumann & Kravic's books on battle weapons of the Revolution and you'll occasionally run across something that jumps out at you if you are familiar with symbolism.
Do you have a copy of Madison Grant's book "The Knife in Homespun America"? If so,look on page 9 at what Madison calls "the alligator eye" knife.Even he didn't know what he had here,but any Freemason will immediately pick up on it :winking:.
Last June while at the KRA meeting in Carlisle I had a chance to see the "Clash Of Empires" exhibit at the Heinz Museum/Center in Pittsburg.Outstanding is all that I can say.Anyone with any feeling for our Colonial History should see this exhibit if possible. An observant Freemason with basic rememberances of symbolism will pick up on several things.
Hope this helps a little,
der Forster 32, :hatsoff: