Abstract: A mechanism for releasing one member from another. A piston is disposed partially in the bore of one member and partially in the bore of the other member to bridge the gap therebetween for maintaining attachment thereof. The piston is responsive to a propulsive force for movement forwardly to a second position wherein all of the piston is disposed in the other member. The other member bore has a reduced-diameter portion forward of and adjoining an increased-diameter rearward portion thereby providing a shoulder. The piston has a forward portion and a rearward portion having substantially the same diameters as the forward and rearward bore portions respectively of the other member. A tapered portion connects the piston forward and rearward portions and is impelled on the shoulder when the piston is moved to the second position.