An experimental study of the plasma leaving a coaxial gun is described. The plasma shows a conical shape with a central axial pinch. When a radial magnetic field is applied at the muzzle of the gun, magnetized plasma rings are formed. Under certain conditions the central pinch shows a helical instability, resulting in a considerable increase of the poloidal magnetic flux in the plasma rings. Different types of discharges are described, associated with the occurrence of a ``short‐circuit'' in the gun. During the decay of the plasma, magnetoacoustic oscillations are observed.