A report on German MG-151 15-mm and 20-mm aircraft machine guns, from Tactical and Technical Trends, No. 30, July 29, 1943. [DISCLAIMER: The following text is taken from the U.S. War Department publication Tactical and Technical Trends. As with all wartime intelligence information, data may be incomplete or inaccurate. No attempt has been made to update or correct the text. Any views or opinions expressed do not necessarily represent those of the website.]

GERMAN MG-151 TYPE 15- AND 20-MM AIRCRAFT WEAPONS A brief description of both of these types of aircraft gun was reported in Tactical and Technical Trends, No. 12, p. 2. a. MG 151/15 Additional information about the 15-mm weapon indicates that it is of Mauser design, manufactured by Rhein Metall, well constructed, and with excellent performance. As noted in the previous description, this gun (as well as the 20-mm) is cocked and fired electrically; the cocking mechanism consists of two sprockets and a roller chain driven through a train of gears by a small high-speed motor. Subsidiary hand cocking is done by a chain ending in the cross-bar at the rear end of the breech cover. There is no applied safety device as electrical safety only is provided. Provisions are for automatic firing only. The firing is by electrical solenoid operating a sear release. The gun is recoil operated unassisted by muzzle blast. The system of feed is by disintegrating metal link belt. There is a resilient front mounting comprising a cylinder sliding in an outer housing and acted upon by four double-acting buffer springs and 2 buffer brakes. The sliding cylinder has 2 hooks which engage with lugs on the gun casing to lock the gun and mounting together. The rear of the gun is supported by 2 annular bushings mounted in a bracket and sliding on 2 cylindrical rails attached to the aircraft structure. b. MG 151/15 and 151/20 Compared Sometimes it is erroneously supposed that the MG 151/15 and the MG 151/20 are the same gun fitted with interchangeable barrels. Though of basically identical design and similar appearance, they are separate and distinct weapons. The MG 151/15 was first encountered, installed in the Heinkel 115. German aircraft now mounted with the MG 151/15 as standard armament are the following: JU-88 (night fighter), DO-217, HS-129. In all cases the fixed gun is mounted in the nose. Each of the following flying boats carries one or more of these guns in hydraulically-operated power turrets; BR-138-B, BV-138-C, DO-18-D, DO-18-G. Construction details of the 151/15 are listed below. Caliber (nominal)   15 mm (0.591 in)      Length (overall)   75 1/2 in Bore;   Barrel;     No. of grooves 8   Weight 23 lb 14 oz   Pitch 1 turn in 16 in   Length (overall) 49 1/4 in   Direction Right hand Rate of fire;   Weight (including     AP 740 rpm elec. control) 84 lb 1 oz   HE 680 rpm Some of the differences between the 15-mm and 20-mm caliber 151 type of machine gun are shown in the following summary.       15-MM Caliber       20-MM Caliber   Barrel:    Length  49 1/4 in  43 1/2 in    Weight  23 lb 14 oz  22 lb 14 oz    Pitch (rifling)  1 turn in 16 in  1 turn in 23 in    Groove (width)  .157 in  .210 in    Groove (depth)  .009 in  .0105 in Weight  84 lbs 1 oz  93 1/2 lb Length (overall)  75 1/2 in  69 5/8 in In addition, the 20-mm has a shorter chamber and a slightly larger diameter at front end; the body is strengthened on the underside; the housing buffer is different in design internally, and slightly longer. Also, the feed block, the cartridge stop, the electrical layout for cocking, and the bullet guide in front of the feed pawl vary in the two weapons.

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