Abstract: The present invention discloses a blank firing attachment for gun tubes of utomatic or semi-automatic weapons when firing blank cartridges. The attachment includes a flash suppressor having milled axial slots threadably attached to the gun tube, a slidable cam pivotally mounted to a collar threadably attached to a shaft containing a restricted passage for gas flow from the gun tube, and a number of locking lugs pivotally connected to the collar. Axial movement of the shaft causes the lugs to engage the axial slots and the shaft to engage the gun tube end, thereby restricting gas flow from the gun and providing back pressure to permit automatic or semi-automatic firing of the weapon when using blank ammunition. Thus, the attachment is made compact and is fireable in all modes for various weapons, including M231 weapon.