This sunburst type of countermark on a very worn Irish 1/2 penny dated 1805 has baffled me for at least 4 decades. Usually a sunburst countermark is indented into the coin's surface whereas this sunburst is raised up through the harp on the reverse being pushed up from behind by a slightly rounded large punch of some sort against the bust of King George III. This has flattened his bust into obscurity.

By defacing the royal bust along with the Irish harp in one stroke I would have to guess that this might serve a political message - or maybe it is a membership or even a commercial token?