Here's a few more pics,after shooting the AR today, I had a mooch about in the undergrowth and pulled out two similar panels, with traces of white paint and a bracket hung piece of inch thick steel.

Clearly armour piecing .303 has been fired at at it, looking at the penetrations into the steel, plus some stomping with .50 AP too, I should imagine.

Located with them is some sort of hanging arm, see pics.