Right so this is not that bad
So first you need to get the blundergat which you can get in the box or you can build one by following the quest
See this link for details
Once you have a blundergat next go to the warden's office
You get the magmagat by putting it in the fireplace in the warden's house killing zombie's and taking their souls to fill it then you run back to spawn to the room with the furnace and the blade trap make sure to keep hitting the barrels on the way or your gun will revert back to the regular blundergat
And lastly the acidgat you can obtain this by finding the parts around the map
Part #1: Transverse Tunnel – Found on the ground in the tunnel linking New Industries to the Power House.
Part #2: Sally Port – Found in the sideroom on the path to the Warden’s Office area. Requires the Warden’s Key to unlock the metal gate.
To get the Warden’s Key, activate both Power Switches to summon Brutus. Defeat him, and you’ll be able to collect the Warden’s Key from his body.
Part #3: Infirmary – In a locked cabinet in the corner of the Infirmary. Once again, you’ll need the Warden’s Key to unlock the cabinet and collect the glowing green container.
Then just kill the warden with each of the guns in any order