Rifle vs. Gun

[Joe W]

Not only the Marine Corps uses the term "rifle" for a firearm such as the U.S. Rifle Cal. .30 M1, so does Webster. "RIFLE - A firearm with a rifled bore, designed to be fired from the shoulder. b. An artillary piece or Naval gun with such spiral grooves. ( by the way, is the use of the term "Naval gun" by Webster an oxymoron ? )
Shotguns are also "guns" not "rifles".

But I must admit, but not to my former D.I ., that I do find myself, on occasion, calling a rifle a gun, but when I do, I know I made a mistake. Semper Fi