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The 4.2 inch M30 mortar was a rifled muzzle-loading weapon designed for high-angle fire.

Weight (with base plate, base ring, and sighting equipment): 626 lb.
Barrel assembly: 158 lb
Standard assembly: 58 lb
Bridge assembly: 151 lb
Rotator assembly: 57 lb
Base plate: 108 lb
Base ring: 100 lb
Sighting equipment: 4 lb

Range: 6,500 yards

Ammunition: Ammunition for the M30 (T104) was issued as complete rounds, similar to those for the 4.2 inch M2, but had extended length of cartridge container and larger propelling charge. The round consisted of shell, fuze, propelling charge, and ignition cartridge. When fired, the shell was stabilized in flight by rotation transmitted to the shell by means of the pressure plate expanding the rotating disk on the base of the shell thus forcing the disk to engage the rifling in the bore. The shell, which had a deep cavity and suplementary charge, was fitted with a point detonating fuze. The ignition cartridge was housed in the cartridge container extension and was held in place by the striker nut which contained the striker. The propelling charge consisted of a number of increments of propellent powder in the form of square sheets assembled on the cartridge container. When the round was inserted into the bore and released, it slid to the bottom where the firing pin drove the striker into the primer of the ignition cartridge. Flame from the ignition cartridge flashed through vents in the cartridge container extension to ignite the propellant, thus firing the round.


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