Mont. Code Ann. § 46-5-313

If a firearm possessed by a law enforcement agency was not purchased by the agency for agency use, if it is legal for a private person to own and possess the firearm, and if the legal owner cannot be determined by the agency, the agency may not destroy the firearm and shall sell the firearm to a licensed dealer. The proceeds of the sale must be deposited in the general fund of the governmental entity of which the agency is a part.