Ammunition. Ammunition or cartridge cases, primers, bullets, or propellent powder designed for use in any firearm other than an antique firearm. The term shall not include any shotgun shot or pellet not designed for use as the single, complete projectile load for one shotgun hull or casing, nor (b) any unloaded, non-metallic shotgun hull or casing not having a primer.
27 CFR § 478.11
When used in this part and in forms prescribed under this part, where not otherwise distinctly expressed or manifestly incompatible with the intent thereof, terms shall have the meanings ascribed in this section. Words in the plural form shall include the singular, and vice versa, and words importing the masculine gender shall include the feminine. The terms includes and including do not exclude other things not enumerated which are in the same general class or are otherwise within the scope thereof.