The Glock 21 is a pistol manufactured by the Austrian company, Glock. The G21 is a large frame Glock modeled after the Glock 20 and the G21 fires the .45 ACP ammunition.
The Glock 21 uses a minor modified Glock 20 frame, magazine, modified slide and .45 ACP barrel, but these differences are not significant and the G21 does look precisely identical to a Glock 20. The G21 is a very popular law enforcement and sports pistol in the United States, because of its proven reputation for rugged durability, its popular and effective chamber in the .45 ACP cartridge and its 13-round magazine capacity.
Like most .45 autos the Glock 21's large frame size makes it some what uncomfortable for numerous people but the pistol is well suited for those with larger hands.
The G21 has undergone 3 major revisions since its introduction and current models are often referred to as 3rd generation Glock 21s.
The difference between the Glock 21 and the compensated Glock 21C is that the slide and barrel are compensated on the C model to significantly reduce muzzle climb while firing the pistol.
Additionally, there are Glock 21 "Tactical" (Extended/Threaded Barrel) and "Mariner" (underwater firing capability) / Models of this pistol available in the Philippines.