In a self-loading semiautomatic or fully automatic gun, a gas-operated reloading system uses the pressure of the gas of the burned propellant from the cartridge bled off the barrel to operate the locking system and cycle the firearm.
A long-stroke gas-operated system uses a piston to operate the firing cycle of the gun. The system is called “long stroke” because the piston is permanently or mechanically fastened to the op rod and then to the bolt / bolt carrier in such a way that the piston itself travels with the carrier during the whole functional cycle.
The most famous gun using the long stroke system is obviously the AK47, but many other guns, such as the M1 Garand rifle, FN MAG and Minimi machineguns also use it.
The main advantage of the long stroke system is that, since bolt carrier, op rod and piston are assembled in a single part, and move during the whole firing cycle, the added mass of the assembly increases momentum and therefore increases reliability of the firing cycle without adding to the total weight of the firearm.
Main disadvantage is a lower inherent accuracy, due to a larger moving mass influencing control of the firearm – especially at the start and ending of the bolt travel – and the gas block acting as a fulcrum lever that heavily influences the barrel during shooting cycle.
To illustrate how the system works, all4shooters.com made a brief video: enjoy!
In the video, the gun we used as an example is a fairly rare SIG Sturmgewehr 540, a 5.56 caliber assault rifle that was the base for the more famous 550 or Sturmgewehr 90 of the Swiss Army. Manurhin manufatured the weapon under SIG license for a short period for the French army as temporary service rifle before the adoption of the FAMAS in the early 1980’s.