Tesla Gun in The Final Reich
After unlocking the Bunker and Salt Mine, go inside the Command Room and interact with the crank until it stops. Then, go inside the Emperor Room and interact with the machine in front of Barbarossa's statue. Next, continue killing zombies near the machine to charge it up. Keep killing zombies in the nearby area until the Mind Power Machine floats into a hole in the ceiling. After charging the Mind Power Device, go to the Command Room and interact with the button on the upper section of the room to cause the Mind Power Device to start moving; the machine will come to a stop at certain locations. You must keep the Mind Power Device moving. To do this, stay inside the red circle on the ground and continue killing nearby zombies to charge the MPD again. Eventually, the MPD will move near an Electrical Generator, right next to the Schnellblitz Machine. After a short while, the MPD will infuse with the Electrical Generator and shoot out a piece of the weapon. After obtaining the gun's part, the Mind Power Device will start moving again. While following it, kill zombies inside the red circle on the ground until the MPD reaches the Mortuary Generator. You then need to wait for a while to acquire the Tesla Canister from the inside of the generator. After that, go back to the Command Room to find a special zombie on the upper section of the room. Kill this special zombie and grab its head. Once you have both parts, go to the machine in the middle and place them to get the Tesla Gun.