An adaptor for use with a flash suppressor on a gun barrel in order to allow the gun to repeatedly fire blank rounds of ammunition. The adaptor has a stem that chokes the flow of gases from an exploding round in order to create a back pressure. A body is used to couple the stem to the flash suppressor and permit a cap to be threaded to the body. The cap urges the stem into the throat of the flash suppressor when tightened to the body while the body grips the flash suppressor to hold the stem and cap in place. Belleville washers in the cap pre-loaded and urge the stem into the throat and hold it there securely during repeating firing of the gun.