The Heckler & Koch UMP was developed and manufactured by Heckler & Koch and is classed as a submachines gun. Various agencies have adopted the weapon such as the U.S. Customs and Border Protection. Heckler & Koch UMP was originally developed as a successor to the MP5, though both still remain in production today.
The Heckler & Koch UMP is a blowback-operated, magazine-fed submachine gun firing from a closed bolt. As originally designed, the UMP is chambered for larger cartridges than other submachine guns like the MP5, to provide more stopping power against unarmored targets than the 9x19mm Heckler & Koch MP5 provides. A larger cartridge produces more recoil, and makes control more difficult in fully automatic firing. To solve this, the cyclic rate of fire was reduced to 650 rounds/min (600 rounds/min for the UMP45), which makes it one of the slower firing submachine guns on the market.
The UMP9 (the 9x19mm version of the UMP) is almost 0.45 kg (almost 1 lb) lighter than its Heckler & Koch MP5 counterpart. The weight of the weapon is reduced as it is predominantly made from a polymer construction and the number of parts susceptible to corrosion due to this.
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The UMP is available in four trigger group configurations, featuring different combinations of semi-automatic, 2-round burst, fully automatic, and safe settings. It features a side-folding buttstock to reduce its length during transport. When the last round of the UMP is fired, the bolt locks open, and can be released via a catch on the left side. The standard viewing sights comprise an aperture rear sight and a front ring with a vertical post. It can mount four Picatinny rails for the attachment of accessories such as optical sights, flashlights, or laser sights. Vertical foregrips can be attached to the bottom rail for increased controllability during burst and automatic fire.
There are three versions of the UMP: the UMP45, firing a .45 ACP cartridge; the UMP40, firing a .40 S&W cartridge; and the UMP9, firing a 9x19mm Parabellum cartridge. Apart from the different chambering, all versions feature the same basic design, the most noticeable difference being the curved magazine used on the UMP9 (whereas the UMP40 and UMP45 use a straight magazine). All three versions of the weapon can be converted to any of the available chamberings via replacement of the bolt, barrel, and magazine.
The USC or Universal Self loading Carbine is a semi-automatic version of the UMP that could be owned by private citizens for sporting purposes. It was designed following the Assault Weapons Ban of 1994 in the United States and conforms to those standards. Changes from the original UMP include a “thumbhole” type stock and grip (versus the pistol grip of the UMP), longer barrel, limited 10-round magazine, and semi-automatic only trigger group and action. Originally available in gray, as of early 2007 the USC comes only in an all-black finish.