|Rifles get there name from the rifled barrel. |
A rifle is also shot from the shoulder, where the buttstock rests against your shoulder
For a Rifle to be considered one the barrel must exceed 16 inches and the entire gun must exceed 26 inches. These rules are enforced by the ATF (Bureau of Alcohol, Tobacco, Firearms and Explosives) under the National Firearms Act (NFA). If it's shorter than that you need to pay a tax and in some states, you can go to jail.