shoulder weapon

or shoul·der gun

[ shohl-der wep-uh n or shohl-der guhn ]
/ ˈʃoʊl dər ˌwɛp ən or ˈʃoʊl dər ˌgʌn /

noun

a firearm that is fired while being held in the hands with the butt of the weapon braced against the shoulder.
Often shoul·der arm.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019