SIG MKMS

The SIG MKMS was sub-machine gun designed by Schweizerische Industrie Gesellschaft (SIG) company in Neuhausen during the early 1930s and was first introduced in 1933. It was designed for the military and to increase firepower it had a larger capacity magazine as well as a longer barrel, one that would be more common on an assault rifle. Only 1,228 of these guns were produced.

Design
The SIG MKMS made use of an ingenious delayed blowback action which kept the cartridge within the chamber long enough for the pressure within the barrel to decrease to a safe level. The delayed blowback action was made up of a two-part bolt which was designed by Gotthard End. It was also the first ever personal weapon to have a folding magazine so the longer than usual magazine could be stored horizontally within the wooden stock. This made transportation during non-combat movement easy and much less difficult compared to some guns without folding magazines, yet when trouble did arise, a simple catch system would release the magazine allowing normal firing to commence.

Delayed Blowback Action
The locked-breech blowback system mirrored that of John Pedersen's Remington Model 51 only with a locking recess above rather than below the bolt. The longer barrel of the MKMS required either a bolt of greater mass or a locking system. When the firearm is in battery, the breech block rests slightly forward of the locking shoulder in the frame. When the cartridge is fired, the breech block and bolt carrier move together a short distance rearward powered by the energy of the cartridge as in a standard blowback system. When the breech block contacts the locking shoulder, it stops, locking the breech. The bolt carrier continues rearward with the momentum it acquired in the initial phase. This delay allows chamber pressure to drop to safe levels while the breech is locked and the cartridge slightly extracted. Once the bullet leaves the barrel and pressure drops, the continuing motion of the bolt carrier cams the breech block from its locking recess, continuing the operating cycle.

Other Features
There was no fire selector switch for single or automatic fire. This was gauged by the force of pull on the trigger. A short pull was for single shot and a long pull was for automatic fire. This was also one of the first sub-machine guns that had an integral dust cover on the magazine housing.

Variants
There were 3 variants of the MKMS. There was the shortened barreled MKPS which still used the overly complicated two-part delayed blowback action. This was designed for the police market. In 1935, SIG then created the MKMO and the MKPO. The MKMO had the long barrel of the MKMS but had a more conventional single-part blowback action while the MKPO had the shortened barrel as well as the single-part bolt blowback action. Both also fired from open bolt manual safety which was located on the left side of receiver.

Specifications of MKPS

Both MKMS and MKPS submachine guns were somewhat complicated and made to extremely high standards, so the price was high and sales were low and thus production was stopped in 1941.

Sighting Flaws
The sights for both the MKMS and MKPS were both fully manually adjustable but could be calibrated from 100 metres to an optimistic 1000 metres. This led to much confusion with accuracy often found wanting in young soldiers who couldn't operate the sights properly.

Comparable Weapons

 * Remington 51
 * SIG MP-48