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,
Construction details of the 151/15 are listed below.
|Caliber (nominal)|| ||15 mm (0.591 in)
||Length (overall)|| ||75 1/2 in|
| 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;|| |
|| 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 |
|| 49 1/4 in||
|| 43 1/2 in|
|| 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|
|| 84 lbs 1 oz||
|| 93 1/2 lb|
|| 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.