"The Astra Modelo 1921 (famously known as the Astra 400) in its native 9x23mm (9mm Largo) chambering with a 6-inch barrel was the standard-issue sidearm of the Spanish military from 1921 through the Spanish Civil War. It is highly regarded by surplus collectors for its distinctive tubular, ""squirt-gun"" profile and its incredibly robust, over-engineered all-steel construction. Unlike almost all other military pistols firing a full-power service cartridge (which use a locking barrel system), the Astra 1921 is a straight blowback weapon. To keep the action safely closed until chamber pressures drop, Astra utilized an incredibly heavy slide paired with an exceptionally stiff, heavy-duty recoil spring wrapped directly around the barrel."