A spring air gun includes a reciprocable piston and a slide for cocking the piston. The slide is movable between forward and rearward positions. A piston rod is connected to the slide and is slidably mounted within a piston tube which is connected to the piston. A pair of springs are concentrically mounted on the piston tube, and the forward end of each spring engages the piston. The rearward end of the inner spring engages the slide, and the rearward end of the outer spring engages the frame of the gun. A detent maintains the slide in the forward position, and a sear maintains the piston in the cocked position and is engageable with the detent for preventing the slide from moving rearwardly until the gun is fired. The gun is fired by pulling a trigger, which releases the sear from the piston. The detent can then be moved to allow the slide to be moved rearwardly to cock the piston. When the slide is not in the forward position, the detent prevents the trigger from being pulled.