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 – approx. 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/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 Panzerjäger Tiger (P) 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. Hence, the Krummlauf was fitted with the StG44 Gun and used by the tank crew as a machine gun.