The MKMO – M = Maschinen, K = Karabiner M = Militär, O = Oben (Top ejection) – was designed for the military and to increase firepower it had a larger-capacity magazine as well as a longer barrel.

Finland purchased approximately 282 of the original MKMO variant, which were used by the home guard, supply units and coastal defense forces in the Continuation War.

[4] The SIG MKMO used a hesitation-locked operating system which kept the cartridge within the chamber long enough for the pressure within the barrel to decrease to a safe level.

This system was adapted by Gotthard End based on a John Pedersen design first used in the Remington Model 51 pistol.

This delay allows chamber pressure to drop to safe levels while the breech is locked and the cartridge slightly extracted.

These versions did away with the Pedersen hesitation lock and operated on the straight blowback system firing from an open bolt.