Carbon buildup on the face of the breech or debris in the bolt raceway could cause a failure to fire, while a dirty chamber could cause a failure to feed. Stoppages were not uncommon, and could occur for a variety of reasons, some as a result of poor maintenance while others were particular to the Sten.

The Sten gun was known to suffer from a number of design faults. The German SMGВ MP40 MP40, Soviet SMGВ PPS-43 PPS-43, and US SMGВ M3 M3 submachine guns were all made with a similar design philosophy to that of the Sten: simple to make, easy to maintain, and cheap to produce. There is no breech locking mechanism, so the rearward movement of the bolt caused by the recoil impulse is arrested only by the mainspring and the bolt's inertia. This means the bolt remains to the rear when the weapon is cocked, and on pulling the trigger the bolt moves forward from spring pressure, stripping the round from the magazine, chambering it, and firing the weapon all in the same movement. The Sten was a blowback-operated submachine gun firing from an open bolt, with a fixed firing pin on the face of the bolt. In terms of mechanical operation, the Sten was also incredibly simple. To this end, the Sten was built primarily of simple stamped metal components and required only minor welding, which meant minimal machining and manufacturing was needed to build one. Unlike the Lanchester, however, the Sten was designed to be as cheap and easy to produce as possible. The design they came up with shared many design elements, such as its side-mounted magazine, with an earlier submachine gun design, the Lanchester (a British copy of the German MP28). Major Shepherd was the inspector of Armaments in the Ministry of Supply Design Department at The Royal Arsenal in Woolwich, while Turpin was the Senior Draughtsman of the Design Department at Enfield. The design of the Sten gun is credited to Major Reginald V. As a result, the guns could not be produced fast enough, and so the Royal Small Arms Factory Enfield was commissioned to design an alternative. However, Thompsons were time-consuming and expensive to produce, being anywhere from $70-200 per unit. At the time, the British had been purchasing large quantities of Thompson submachine guns from the United States. The British military had suffered great materiel losses during the evacuation at Dunkirk, and needed a submachine gun that could be quickly manufactured to help resupply the armed forces.

The Sten was created during a time of desperation. The Sten gun served as the basis for the superior Sterling submachine gun, which replaced the Sten in British service until the 1980s, when it and all other submachine guns were replaced by the ARВ L85A1 L85A1 assault rifle. They had a simple design and a very low production cost, making them effective insurgency weapons for resistance groups, and they continue to see usage to this day by irregular military forces. They were used extensively by both British and Commonwealth forces throughout World War II and the Korean War. The STEN was a family of blowback-operated British submachine guns chambered in 9Г—19mm Parabellum.

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