A firing adapter for a combination gas and recoil operated weapon includes a blank firing barrel attached to the weapon; a piston having a barrel end and an anchor end, the barrel end being reciprocably disposed in the blank firing barrel and the anchor end being fixed to a non-recoil surface; and a gas port formed in the blank firing barrel wherein in a rest position of the weapon, the barrel end of the piston closes the gas port, and in a recoil position of the weapon, the barrel end of the piston opens the gas port.