Gases of combustion vented from the bore of a shotgun barrel in spaced relation to the muzzle travel along one or more passageways externally of the barrel and are discharged externally of the barrel and ahead of the muzzle in a generally transverse direction relative to the barrel axis to create turbulence immediately forward of the muzzle and exert lateral forces on a shot charge after the charge leaves the muzzle whereby the short range shot pattern produced by the barrel is substantially enlarged. A finite, moveable mechanical obstruction projecting into the bore retards the advance of a wad to reduce influence of the wad on the shot charge.

A gas operated auto loading shotgun having an axially elongate magazine tube and a gas operated piston/cylinder coaxially surrounding the magazine tube includes a gas pressure relief mechanism at the forward end of the gas cylinder for venting gases of combustion in a forward direction toward the muzzle end of the gun when gas pressure within the gas cylinder exceeds a predetermined magnitude. The pressure relief mechanism includes two angularly spaced apart vent ports communicating with the interior of the gas cylinder and terminating at valve seats at the forward end of the gas cylinder. Spherical valve elements seated on the valve seats are biased toward the valve seats by an annular flat spring member secured in fixed on the gas cylinder by a single fastener and surrounding an associated portion of the magazine tube.