帮忙找一篇关于“submachine gun”的英文文献

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  MP5 A4 Submachine Gun of Pakistan Military
  
  MP5 A4 is one of the most common gun in the arsenal of our military after G3 and AK47. It is mostly used by SSG for special operations and also used by police and other military personnel. Because of its light weight and small size, it is suitable for urban terrain. A brief design details are given below:
  
  The MP5 is a 9 mm submachine gun of German design, developed in the 1960s by a group of engineers from the West German arms manufac turer Heckler & Koch GmbH (HK). The company, motivated by the success of the G3 rifle developed a group of small arms consisting of four types of firearms (all based on the G3 design layout), where the first type was chambered in 7.62×51mm NATO, the second – using the 7.62×39mm M43 round, third – the intermediate 5.56×45mm NATO caliber and the fourth type – chambering the 9×19mm Parabellum pistol cartridge. The MP5 (short for Maschinenpistole 5) was created within the fourth group of firearms, initially known as the HK54. The primary version of the MP5 submachine gun family is the MP5A2, which is a selective-fire roller-delayed blowback operated weapon. The bolt mechanism consists of a bolt head and bolt carrier. After firing, the rollers integrated into the bolt head are cammed inward against the inclined planes of the barrel extension and locking piece by rearward pressure on the bolt head. As the rollers are forced inward they displace the locking piece and propel the bolt carrier to the rear. The bolt carrier’s rearward velocity is four times that of the bolt head since the bolt remains locked for a short period of time after the initial recoil impulse. After the bolt carrier has traveled rearward 4 mm, the rollers on the bolt head (which has moved only 1 mm) are compressed in, unlocking the bolt, opening the breech, and the two parts continue their backward movement together. Since the 9×19mm Parabellum cartridge is relatively “weak”, the bolt does not have an anti-bounce device, but instead the bolt carrier contains tungsten granules that prevent the bolt from bouncing back after impacting the barrel extension. The weapon has a fluted chamber that enhances extraction by bleeding gas backwards to loosen the spent cartridge from the chamber walls (the bolt is opened under relatively high barrel pressure). A spring extractor is installed inside the bolt mechanism, while the lever-type ejector is located inside the trigger housing (activated by the movement of the recoiling bolt).

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