Glock 21

Glock Ges.m.b.H. developed the Glock 21 as a variant of the Glock 20, designed for the United States market. The firearm was engineered by Gaston Glock using the manufacturer's established polymer-frame technology. It follows the design lineage of the original P80, which entered Austrian service in 1982.

The pistol operates via a short recoil, locked-breech mechanism utilizing a linkless, vertically tilting barrel. This system employs a rectangular breech that locks into the ejection port of a slide milled from ordnance-grade steel. The frame is composed of a nylon-based synthetic known as Polymer 2, which is resistant to temperature extremes and caustic substances. For corrosion resistance, metal parts undergo a nitriding process. The internal "Safe Action" system consists of three independent safety mechanisms—trigger, firing pin, and drop safeties—which automatically disengage during the trigger pull. To accommodate its specific chambering, the barrel features octagonal polygonal rifling rather than the hexagonal pattern found in other models. The slide is lighter than that of the Glock 20 to balance the operating cycle, and the grip is set at a 109-degree angle.

National armed forces and security agencies in several countries have adopted the Glock 21, including the Philippine Marine Corps, the Brazilian 1st Batalhão de Forças Especiais, and the Greek EKAM unit. Within the United States, the New York City Police Department is a documented user. Variants include the Glock 21SF, or Short Frame, which incorporates a reduced trigger reach and shortened heel. The model has transitioned through multiple design generations, including Gen4 and Gen5 versions. The firearm is also rated to fire higher-energy ammunition of the same caliber.