The Sten was an incredibly simple weapon which utilised the system known as 'blowback'. In one second, the Mk.III firing at a rate of 540 rpm, could fire nine rounds. A basic description of the operation of the system is as follows:

1. The weapon is loaded and cocked by drawing back the breechblock or bolt.


2. The sear holds the bolt to the rear, compressing the main spring.


3. Pulling the trigger drops the sear and the spring forces the bolt forward.


4. The feed ribs of the bolt strip the top round from the magazine and force it into the chamber.


5. Once the round is seated in the chamber, the firing pin discharges it.


6. The detonation of the round produces a release of gas which propels the bullet along the barrel.


7.Too much gas is produced to force the bullet from the barrel in time, and so the gas pushes back on the cartridge case, which forces the bolt to the rear.


8.The extractor draws the empty case from the chamber as the bolt moves back, and the ejector expels the case from the weapon.


9. If the trigger is released, the sear rises and catches the bolt, holding it to the rear.


10. If the trigger remains pulled, the weapon will continue to cycle until the magazine is empty.