That's a surprisingly nuanced question actually. But most of the nuance comes from edge cases that aren't very common. According to the ATF: >The term “Rifle”

That's a surprisingly nuanced question actually. But most of the nuance comes from edge cases that aren't very common. According to the ATF: >The term “Rifle” means a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of the explosive in a fixed metallic cartridge to fire only a single projectile through a rifled bore for each single pull of the trigger.