The FAL DSA-58 OSW (OSW standing for "Operational Special Weapon") is a variant of the FN FAL selective-fire 7.62x51mm NATO battle rifle. The DSA SA-58 OSW is equipped with a folding-stock, a shorter 330 mm barrel and a cyclic rate of 750 rounds/minute.
In Rambo, Diaz carries a DSA SA-58 OSW short FAL Carbine with a folding stock and red-dot scope as his personal rifle. Diaz's version has the Type III Metric receiver (with minimal machining cuts). The DSA SA-58 OSW, is offered with the Type I receiver (more cuts, lighter weight, but not as strong). Thus it is suspected that the SA-58 OSW in the film is a build up of a previous FAL Type III receiver with DSA OSW Parts.
The FAL, or Fusil Automatique Léger ("Light Automatic Rifle"), is a semi-automatic/selective fire battle rifle produced by the Belgian armaments manufacturer Fabrique Nationale de Herstal (FN). During the Cold War it was adopted by many North Atlantic Treaty Organization (NATO) countries, with the notable exception of the United States. It is one of the most widely used rifles in history, having been used by more than 90 countries. The FAL was predominantly chambered for the 7.62x51mm NATO round (although originally designed for the .280 British intermediate cartridge) and because of its prevalence and widespread use among the armed forces of many NATO countries during the Cold War it was nicknamed "The right arm of the Free World". A British Commonwealth derivative of the FN FAL has been produced under licence as the L1A1 Self-Loading Rifle.