The K5 was first produced in 1989. It is recoil operated and uses a conventional Browning-type locking system. It is mostly carried by Commissioned Officers in the Republic of Korea Armed Forces. The DP51 is a popular surplus pistol in the west, with an average K5 going for roughly $300. The K5 is getting harder to find, and parts are scarce, but the guns still remain affordable. The Daewoo DP51 has been noted to be similar to numerous other firearms, such as the Smith & Wesson 5906 (whose magazines are compatible with the K5), Beretta 92, SIG Sauer P226, CZ 75, Walther P38, Browning Hi-Power and the Colt M1911A1.
Daewoo engineers first designed the DP51/K5 in 1984 for use by the South Korean military as its main sidesrm. Daewoo was a company that also made a variety of products, including cars, so engineers needed American rifling experts to help them with producing accurate barrels for the DP51. After surplus weapons gained curiosity for their trigger system, in 1989 the DP51 was first mass produced for the general public. The K5 is a compact, lightweight pistol with an ambidextrous safety, claw hammer and a unique trigger mechanism called "fast action". The frame is composed of an aluminum alloy with a matte finish, while the slide is of nitron blued steel. The pistol is well known for looking bulky, but being very light but with good ergonomics.
The "fast action" trigger mechanism allows the hammer to be decocked while still keeping the mainspring compressed. A light pull on the trigger causes the hammer to flick back, after which the pistol would behave in conventional single-action (SA) mode. In other words, the "triple action" pull is the long length of a double action pull with the light weight of a single action pull. The gun can also be fired in regular, more conventional DA/SA configuration, aside from the special triple action/single action function. Triple action is activated by lowering the hammer after cocking it.
The fast action trigger allows for a more accurate first shot due to the lighter weight of the trigger. It is also safer due to the longer trigger travel required to fire the pistol. The factory double stack magazines hold 13 rounds but higher capacity magazines are available. 14 or 15 round Smith & Wesson 59-series magazines are compatible with the DP51 but will protrude slightly.
The pistol also has an ambidextrous safety and three-dot sights. It is also equipped with a firing pin block which (as its name implies) blocks the firing pin from moving forward unless the trigger is pulled.
The DP-51 is a very well-respected firearm, with particular praise reserved for its trigger system, light weight, ergonomics, versatility with magazines, cost and reliability. Some of the more negative comments are directed at mixed results with accuracy and somewhat heavy recoil due to the weapon's lighter weight.
It is also notable that Lionheart industries now makes an updated version of this pistol, the LH9, LH9C, and LH9 MK2 (amongst other variants). The LH9 Mark II is essentially a slightly updated LH9 (essentially a DP51) with a rail. Differences between the updated versions and the originals are mostly formalistic however; Different rubber grips with more aggressive pyramid texture, two-piece spurred hammer style, firearm coating (Cerakote or graphite black finish).