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The Krummlauf (English: "curved barrel") is a bent barrel attachment for the Sturmgewehr 44 rifle developed by Germany in World War II. The curved barrel included a periscope sighting device for shooting around corners from a safe position.
It was produced in several variants: an "I" version for infantry use, a "P" version for use in tanks (to cover the dead areas in the close range around the tank, to defend against assaulting infantry), versions with 30°, 45°, 60° and 90° bends, a version for the StG 44 and one for the MG 42. Only the 30° "I" version for the StG 44 was produced in many numbers.
The bent barrel attachments had very short lifespans—approximately 300 rounds for the 30° version, and 160 rounds for the 45° variant—as the barrel and bullets fired were put under great stress. Another problem besides the short life-span was that the bending caused the bullets to shatter and exit the barrel in multiple fragments, producing an unintended shotgun effect. As a result, weapons designers experimented with small vent holes drilled into the Krummlauf's barrel in order to reduce pressure and recoil, allowing the discharged bullets' built-up gases to be released to slow the bullet's velocity as it turned to exit the barrel. Nevertheless, the Krummlauf's lifespan remained the same. A triangular shield was also added to prevent venting gasses from clouding the mirror and optics.
The 30° model was able to achieve a 35x35 cm grouping at 100m.
One of the biggest drawbacks of the small number (91 conversions) of Elefant casemate-type tank destroyers was that in spite of having an 88mm anti-tank gun, the initial Ferdinand version of the Elefant did not have a forward-facing hull mount machine gun to handle enemy infantry.
The Krummlauf in a Maschinenpistole Vorsatz (P) mount was developed as an alternative close defence weapon for tank destroyers. This mount was fitted to a roof hatch in many Panzer IV/70 (A) vehicles. The tank crew could then attach a StG 44 and use this as a close defence machine gun.