The SPA (short for Sub Pistola Ametralladora) was a prototype machine pistol of Argentine origin. The weapon was a development of the Browning Hi-Power pistol.
Like most countries that manufacture guns, Argentina has also done its share of research trying to come out with a decent (light, compact, accurate, controllable) full-auto pistol. The whole thing started at the Government-owned Fábrica Militar de Armas Portátiles “Domingo Matheu”, in Rosario, Santa Fe Province, in 1974 as an in-house effort. Being an established licensed manufacturer of the FN Browning Hi-Power, the factory found it proper to use it as the basis for what was called the SPA (Sub Pistola Ametralladora, meaning "Sub Machine Pistol").
Since the Hi-Power’s usual 9×19mm cartridge was recognized as being too powerful for a handheld, full-auto, rapid-firing gun, the guys down South decided to use a somewhat milder cartridge, but still capable of producing serious wounds on humans. They chose the 7.63x21mm Mannlicher cartridge long (1905-1916) used in the Argentine Army Austrian-made Steyr-Mannlicher Model 1905 delayed-blowback semi-auto pistols. With an 85-grain bullet coming out of the gun’s 160mm barrel at 312 m/s, the ammo had been locally produced in vast numbers for years and the tooling had been retained for eventual manufacture re-entry.
The resulting SPA involved only twelve new or modified parts, the most evident being the 159mm long barrel which protruded about 40mm from the slide, with 16, 25, and 40 round magazines being made for the single prototype built. The cyclic rate of fire was in the region of 1,000 rounds per minute. The fire selector was a button located immediately above the trigger: pushed from right to left, the pistol fired full auto; from left to right, semi auto.