Abstract: A blank firing attachment for a recoil operated gun. The attachment comprises a barrel (10) having in its length an external shoulder (12). A gas cylinder in the form of a sleeve (13) is slidingly fitted onto the barrel (10) and located over the external shoulder (12). An internal shoulder (14) of the sleeve is located opposite the external shoulder (12) such that the shoulders (12 and 14) together with the surface of the barrel (10) and the sleeve (13) form a gas chamber (24). At least one gas transfer passage (11) connects the gas chamber (24) to the bore (10′) of the barrel (10). A mounting flange (15) with fastenings (19) and locking lugs (20) fix the gas cylinder (13) to a receiver section (23) of a gun.