Okla. Stat. tit. 21, § 1289.5

DEFINITIONS FOR FIREARMS ACT "Shotguns" as used in the Oklahoma Firearms Act of 1971, shall mean any firearm capable of discharging a series of projectiles of any material which may reasonably be expected to be able to cause lethal injury, with a barrel or barrels more than eighteen (18) inches in length, and using a combustible propellant charge, but not to include any weapon so designed with a barrel less than eighteen (18) inches in length unless the overall length of the firearm is twenty-six (26) inches or more. In addition, any "shotgun" capable of firing single projectiles but primarily designed to fire multiple projectiles such as "shot" will be regarded as a "shotgun".