Nice t-shirt, except I'm not convinced that we were really a nation of riflemen. I'm not turning Bellesiles, but at the Siege of Boston, most of the NE militia were musketmen (just like those who defended Breed's Hill - mistakenly known as the Battle of Bunker Hill). During the Revolution, more riflemen came from the frontier of about six states (PA, western-Virginia, KY, TN, NC & SC) than anywhere else.
What is true is that the rifleman led the westward expansion of this country from 1755 onwards.