MG 42 - Design Details

Design Details

The MG 42 is roller-locked and recoil-operated (short recoil) with gas assist. It fires belt fed 7.92mm ammunition from an open bolt.

The roller-locked bolt assembly consists of a bolt head, two rollers, a striker sleeve, bolt body, and a large return spring, which is responsible for pushing the bolt assembly into battery (the locked position) and returning it there when it is unlocked and pushed backwards by the recoil of firing or by the charging handle. As the striker sleeve is movable back and forth within the bolt assembly, the return spring is also responsible for pushing the striker sleeve forward during locking (described below). The bolt assembly locks with the barrel's breech (the end the cartridge is loaded into) via a prong type barrel extension behind the breech. As it is recoil-operated and fired from an open bolt, the weapon must be manually charged with the side-mounted charging handle.

The roller-locked recoil operation functions as follows: two cylindrical rollers, positioned in tracks on the bolt head, are pushed outwards into matching tracks in the barrel extension by the striker sleeve and lock the bolt in place against the breech. Upon firing, rearward force from the recoil of the cartridge ignition pushes the striker assembly back and allows the rollers to move inwards, back to their previous position, unlocking the bolt head and allowing the bolt assembly to recoil, extracting the spent cartridge and ejecting it. The return spring then pushes the bolt assembly forwards again, pushing a new cartridge out of the belt into the breech, and the sequence repeats as long as the trigger is depressed. The MG42 is only capable of fully automatic fire. Single shots are exceptionally difficult, even for experienced operators, due to the weapon's rate of fire. The usual training objective is to be able to fire a burst of no more than three rounds. The weapon features a recoil booster at the muzzle to increase rearwards force due to recoil, therefore improving functional reliability and rate of fire.

The MG 42 fires from an open bolt, meaning the bolt (not just the firing pin) is held in a rearward position when the trigger is not depressed. Depressing the trigger releases the bolt assembly, of which the firing pin is a component.

The shoulder stock is designed to permit gripping with the left hand to hold it secure against the shoulder. Considerable recoil otherwise causes the stock to creep from its intended position. If the weapon is not properly "seated" on the bipod, a prone gunner may be pushed back along the ground from the high recoil of this weapon.

The MG 42 barrel shroud houses a quick barrel change device similar to the Thompson Light Rifle.

The sighting line consists of a ∧-type post or an inverted "V" height adjustable front sight on a folding post and a leaf rear sight with an open V notch sliding on a ramp, graduated from 200 to 2,000 meters (219 to 2,187 yards). There is an antiaircraft rear peep sight hinged on the open rear sight base. An auxiliary antiaircraft ring sight is kept in the maintenance kit, and fitting on the barrel jacket to be used in conjunction with the folding antiaircraft rear peep sight attached to the rear sight base.

Another unique feature of German WWII machine guns (and which continued to be used by the German Bundeswehr after the war) was the Tiefenfeuerautomat. If selected, this feature walked the fire in wave-like motions up and down the range in a predefined area. E.g., being unsure whether the real distance was 2000 meters or 2300 meters, the gunner could make the mount do an automatic sweep between the elevations for 1900 to 2400 meters and back. This sweeping of a given range (Tiefenfeuer) continued as long as the gun fired.