The device aligned with the axis of the barrel of a firearm is configured to equalize, as well as possible, the momentum generated by the projectile and the burnt gases, by projecting a mass of fluid at a given speed in the opposite direction. The device includes a support to be attached to the weapon, a primary valve mechanism, a secondary valve mechanism and a duct for the gases to flow along. The secondary valve mechanism to seal and fill the tank with a pressurized fluid provided by an external system. The primary valve mechanism to seal and expel the fluid in a discharge zone. The device is particularly intended for military applications in order to improve the grouping of shots and to reduce the costs and limitations of using the barrels.