Hey Rainbow Demon, In both movies you see the gun shoot but the blanks do not operate the slide action, In Falcon, When you get the killers view of holding the gun firing at Mr Archer, if you frame walk after the shot, There is no movement or trigger cocking..
In Zardoz. Zed will cock the gun by pulling the barrel back with his other hand. You will see him shoot it several times in other parts, and the blanks do not re-cock the trigger.
I always fault the actors for these prop failures because of their unwillingness to really 100% commit to the part and Use real bullets..