Abstract: A mechanism for controlling the powder impact force on a projectile in an impact dissipating device includes a stop member having a projecting stop portion which can be engaged with a stop ring of a piston. A base portion of the projecting stop portion includes a substantially ellipsoid guided face having linear stop edes formed on both longer sides of the guided face. The mechanism also has a stop rod with a step-shaped portion on top which can be engaged with the stop edge. A threaded hole is provided on the lower portion of the stop rod. A control rod has a front end provided with a rotation portion and, adjacent the rear of the rotation portion, a securing ring is formed at the periphery of the control rod. A threaded portion is provided at the rear end of the rod and is threaded into the threaded hole of the stop rod.