Near the end of the movie after Simon infiltrates the Kremlin, he chloroforms a guard and takes his weapon. It appears to be an AKS-74u which is characterized by its short barrel. After he shoots the chandelier and runs through the corridor, he walks into the President's room and the gun he holds in his hands has a barrel that has suddenly grown about 6 inches longer and has sprouted a gas block. As if the shot of him holding the weapon wasn't enough, he sets the gun down on the bed so everyone can get an even closer look at his magical AK.