Following the stairs in the third reverse fire chamber you will find a wooden-floored room containing a small gun. This is a specialised piece of artillery known as a "carronade," after the Carron Iron Works in Falkirk Scotland. The ammunition used here was canister shot: a tin can filled with metal balls, each the size of a golf ball. Upon firing, the metal container disintegrated and the metal balls spread out along the length of the west ditch.

The hole through which the gun fires offers a possible way into the fort for an enemy. To prevent this, an extra ditch was dug in front of the chamber and the iron gates at the entrance to the reverse fire chambers would have been locked during an attack.

Please return to the surface through the tunnel by which you entered, and then continue through the door on the left-hand side.