I've seen underweight, bronze-coloured George III half-crowns and shillings before. My initial thought was that they might have been similar to Irish James II 'gunmoney', but George III had no need to issue base-metal gunmoney, that leaves the possibility that they are either extremely rare patterns, or else contemporary counterfeits, and considering the style of the ones I've seen looked at seemed distinctly 'off' compared to the genuine article, in addition to the fact I've seen them turn up on a couple of occasions, suggests to me that they are contemporary fakes using base metal with very little intrinsic worth. It isn't that uncommon to see 1920-1946 50% silver coins looking very 'bronzy' because of their comparitively high copper/silver ratio, but as a George III halfcrown is supposed to be made of .925 fine sterling silver, I don't see how a genuine one could get to that coppery-looking state unless it was really dirty or something...
I've just come across an 1818 copper half crown 12.4g. It came to Australia from the UK with a returning soldier in the 1940's along with some other 19th C French and Middle Eastern coinage. Unfortunately it's not in fine condition but you can certainly rule out contemporary forgery because of its providence.
but you can certainly rule out contemporary forgery because of its provenance. I don't see why. It came from Britain and there are quite a few of them around. I think I have one somewhere, and if it is here now it must have been in England in the 1940s as well, and other examples would have been available for sale or as odd keepsakes. In the 1940s there would even have been some well worn genuine examples in circulation.
