[motto]

There is a weight inside the vertical part of the tube. The cable is attached to this weight and comes out of the tube at the top of the bend and around a pulley. It runs across to another pulley on the end of the horizontal section of tube then down to a cradle which the gun sits in.
I have not seen a gun mounted so cannot tell you exactly how or where the cradle locates but from memory it consists of a bar with a 'U' shaped hook at each end as though the barrel of the gun could sit in it.

David