I'm not sure about an AK-47, but an ar-15 needs a blank firing adapter to cycle the action when blanks are used. It is a device which attaches to the muzzle to increase gas pressure.
If blanks were used, there would likely be something over the muzzle.
Back in the "Old Corps", a field expedient BFA for an M-16 could be had by firing a blank, racking the operating handle, and catching the spent case. One would then use a bayonet to cut the base off the empty, and then use the bayonet to unscrew the flash hider. You would then put the base, primer side up, on the end of the muzzle, and screw the flash hider back down. One would then point the weapon in a safe direction and use another blank to blow out the primer, and the restriction of the flash hole was enough to cycle the action. Since we were the first squad of the 2nd platoon, we always got to be the Aggressors, and probably fired 10 times the blanks of the rest of the Battalion.
(If you forgot and fired a live round, you caught the bolt carrier group under the right eye...)