Abstract: A gas cycling firearm comprising a barrel having a breech end, a muzzle end, an inner surface defining a bore having a bore axis, and an outer surface, wherein the muzzle end is spaced a length L from the breech end, the barrel further having a port providing a fluid path between the bore and the outer surface, the port having an axis that intersects the bore axis at a position P from the muzzle end, where P is less than or equal to ? L; and a gas flowpath extending between the gas port and the piston system, the gas flowpath having a length G and a volume V, wherein G is greater than ? L.

Abstract: An adjustable gas valve having an annular body with an inner surface defining a gas chamber and first and second annular end surfaces defining first and second openings of said gas chamber, the gas valve further having outer surface and at least one gas channel extending between the inner surface and the outer surface providing a gas communication path from the outer surface to the gas chamber, wherein said at least one gas channel is orientated to direct fluid egressing from the channel into the chamber along the inner surface. The invention further includes a regulator occupying a portion of the chamber to define a chamber operating volume, the regulator having at least one outer diameter corresponding to an inner diameter of the passage to substantially inhibit gas flow from the pass through the second opening.