Medieval Trebuchet by apengstrom, from Kingdom of Artania Server. Visit our website at http://www.kingdomofartania.com/
To load, fill the front with 6 TNT on each side, and 1 TNT in between the empty space in the cobble at the top. Press the button on the wood first, then the button on the cobble between 2-3 seconds later. You have to time it right, or you'll blow up the front of your trebuchet with your ammo! :)
Use the switch to push TNT down if needed.