The Mondragón Modelo 1908 was a gas-operated rifle with a rotating bolt using a cylinder and piston arrangement, a design considered unusual at the time. The bolt was locked by lugs in helical grooves in the receiver. A switch, located on the charging handle, would disengage the bolt from the gas system, allowing the firearm to effectively operate as a straight-pull bolt-action rifle. The Mondragón Modelo 1908 rifles were fitted with a bipod. In addition to the knife bayonet introduced with the previous rifles, Mondragón designed a spade bayonet for use with the Modelo 1908, for which he filed a patent application (No. 631,283) on June 6, 1911.