A gun device includes a housing having a gas supplying passage communicating with an inner chamber of the housing for coupling to a pressurized gas supplying source, a feed tube attached to the housing for feeding a bullet into the housing, a tubular member rotatably received in the housing and having an opening communicated with a bore of the tubular member for aligning with the feed tube and for selectively receiving the bullet into the bore of the tubular member. The opening of the tubular member is movable or disengageable from the feed tube when the tubular member is rotated relative to the housing for preventing the other bullet from entering into the housing.