A compressed gas regulator of a piston type is disclosed in which a regulator is configured with an input valve situated entirely inside a compressed air canister, which regulator is then attached to a paintball gun, marker or other device for providing discrete charges of gas at a predetermined pressure to the attached device. The overall size and weight of the regulator are minimized, which allows increased capabilities to the user. A regulator overpressurization port vents behind a conventional safety gauge for safety purposes. Fill, gage, and canister overpressurization rupture ports are interconnected with a fill channel that extends from the canister to the ports without intersecting or interfering with the regulating components within the regulator. The input valve seat face is surrounded by a shallow generally conical surface within an input plenum. The shallow generally conical surface extends at approximately 5 to 15 degrees.