We can play semantics all night long, but a sniper could use a coat hanger and still be called a sniper.
A gun by all modern definitions is anything capable of firing an explosive propelled projectile of any size or caliber.
Your term "large" is entirely unsubstantiated, and under your definition a Mortar would also be classified as a gun, which it's not.
Shotgun, a gun that fires shot. machine gun, a gun that is driven by a machine, sub machine gun etc, your definition is wrong, it may have rang true in 1800, but today it's not.
Either way, we can be sure that browniee is not human trafficking marksmen and we should stop devolving his thread into an anorak convention.
That fps ruling is more than a little bit stupid though.