1807 proof halfpenny.
I suspect this may have originally formed part of a set in gold, silver and copper, with possibly also a bronzed and aluminium example. The rims have been filed on this coin, and are similarly filed on the gold piece. Maybe 10 years ago, I saw a copper proof with filed rims. All this suggests they were done as a one-off on request from one of Taylor's customers. The filed rims aren't restricted to the 1807 either as my Wiener pattern shilling in copper (ESC 1383) also has the rims filed and again is the only example I am aware of. The question is who asked for them? Murdoch?