Use the Naturalized Ammunition to take control of the Death's Door Fel Cannons. Use them to destroy both the South Warp-Gate and the North Warp-Gate. Then, use the Druid Signal to call out to an Evergrove Druid to report your success.
1x South Warp-Gate Destroyed
1x North Warp-Gate Destroyed
Now that the ammunition can affect the Burning Legion, it's time for you to use it.
There are two warp-gates, which are used for teleportation and enhancement of the void terrors. One is in the south and the other in the north, and each is within range of a fel cannon.
Use the naturalized ammunition to take control of each fel cannon and destroy the warp-gates.
Attack the gate with artillery to begin, and be prepared to kill its defenders to keep the cannon alive if necessary.