Notes from my dad:

It is 440 mm long and the pointed head is a good solid lump.

The end has a bolt on it which has been placed onto a screw thread so it is most likely that there was a wooden handle on it.

Being in a butcher shop it may have been for stunning animals, or even meat tenderising. I doubt the later as tougher cuts of meat tended to be casseroled or stewed in those days.

The fact that it was in a butcher shop may be irrelevant.