Okla. Stat. tit. 21, § 1289.3

Definitions for Firearms Act and Self-Defense Act - Pistols or handguns. DEFINITIONS FOR FIREARMS ACT "Pistols" or "handguns" as used in the Oklahoma Firearms Act of 1971 and the Oklahoma Self-Defense Act shall mean any firearm capable of discharging single or multiple projectiles from a single round of ammunition composed of any material which may reasonably be expected to be able to cause lethal injury, with a barrel or barrels less than sixteen (16) inches in length, and using a combustible propellant charge, but not to include any firearm with an overall length of twenty-six (26) inches or more, flare guns, underwater fishing guns or blank pistols.