Well.... I hate to belabor the obvious, but a rifle is a gun. I could prove it in any number of ways.
Why, just the other day I saw an issue of Guns and Ammo and it had a bolt action rifle on the cover. How did that happen if a rifle is not a gun?
I could shoot you with a rifle and if you called the cops and told them, or any other human being alive, "I just got shot with a gun" they wouldn't refuse to prosecute me because they knew my defense attorney would have the case tossed out over your confusion of what I just used to shoot you.
A rifle is a specific kind of gun. A bolt action rifle is an even more specific kind of gun. A pistol is a gun, too. Gun is one of the most versatile terms you'll come across in life, second perhaps only to f*ck.
If a gun can't have rifling, why do we all know battleships are well armed with guns and not rifles?
And why is no one ever shot with a low powered rifle? All I ever hear is people being shot with a high powered rifle. I guess it's just like why no one is ever whelmed.
