What is a Rifle? The ATF Definition

Defined Under Federal Laws: 18 U.S.C., § 921(A)(7) and 27 CFR § 478.11

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.

The illustration shows the primary characteristics exhibited in the rifle category. Since rifle configurations differ significantly, various models in this classification may exhibit any of the illustrated components in a revised configuration but not necessarily all components shown will be incorporated in any one given design.

RIFLE CLASSIFICATION 

Defined Under: 26 U.S.C., § 5485(a)

For the purposes of the National Firearms Act, the following definitions are used to define and verify the different types of firearms:

§ 5845(c) — The term “Rifle Unalterned” 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.

§ 5845(a)(3) — The term “Altered Rifle” means:

A rifle having a barrel or barrels of less than 16 inches in length;

§ 5845(a)(4) — The term “Over All Length Altered Rifle” means:

A weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length;

For more on terminology and nomenclature of rifles, please click:

Firearm Terminology & Nomenclature: Lever Action

Firearm Terminology & Nomenclature: Slide/Pump Action

Firearm Terminology & Nomenclature: Top Break Action

Firearm Terminology & Nomenclature: Self Loading Action (Semiautomatic)

Firearm Terminology & Nomenclature: Bolt Action

All Information Taken From ATF website:
Firearms Verification -- Gun Control Act Definitions