Sketchy 1806 Half Penny

Well, if it's thicker than normal but has an identical diameter, that should result in a higher volume than normal. If the density were the same because the alloy is the same, that then suggests that your coin should be heavier than average. But it isn't. Your coin is underweight. I would be quite suspicious about that.

It looks OK to me, and even in 1806 it would hardly have been worthwhile to make an accurate forgery of one of these 'new' halfpennies, as the pre-1776 halfpennies that were still in circulation were much easier to forge (and there were lots of forgeries in circulation). I don't know if anyone's ever done a detailed study of these coins, but I'd imagine that there could have been variations in the planchette thickness and weight, as it was the first date of a radically redesigned coin and the cons were not struck by The Royal Mint but were contracted out to the Soho Mint in Birmingham. Wikipedia gives the weight of these halfpennies as "9.2-9.8 grams", indicating that there may be a considerable variation.

Thank you all for the replies, especially NumisRob for the information!

I'm intrigued! I've got what I think is a contemporary forgery. It's dated 1806 but on a 1799-sized 31mm blank and under weight for that size blank at 9.2 grams. Edge detail the same as Hondo's. It's just this minute occurred to me that as the 1806 series was struck because price of copper went through the roof, perhaps Matthew Boulton was trying a few ideas out. Or perhaps somebody with inside information was "trying it on", which is my current bet. Who knows? I feel a visit to Brum Museum might come in handy...

Yes. It's about 7.15am here so I'll try to upload some pics in about 12 hours - busy day ahead!

Quite an odd duck. It looks almost as though it were somewhat flattened. Very soft strike, for sure. It has the expected concavity and engrailed edge.

Given the persistent issues Boulton & Watt had with getting good quality planchets at Soho it may just be due to soft copper that would have resulted in spreading and consequentially a weak strike since the striking force was being applied over a larger surface area.

According to Peck, 1806-dated dies were still in use after 1806 and were kept in use concurrently alongside 1807- and 1808-dated dies, so that merits being taken into consideration here as well.

Trial strike is a possibility but the only thing even close would be the 3rd issue G.III Soho halfpenny (1799) at 30mm/12.6g and this is too underweight so I'm going to cast a vote in favor of the former theory.

Anything's possible!

One thing I would take into consideration would be if there are any other known examples matching your coin's specifications, which might lend more credence to the possibility of a pattern issue or trial strike.

There were proofs issued (gilt copper/gilt bronze) but they are always fully struck up in addition to being rather scarce.

It wouldn't be too far out of the ordinary if it were found to be a trial piece. Both Heaton's Birmingham Mint and Soho Mint struck a staggeringly large number of different token and coin designs and there are dozens of tokens known with muled obverse/reverse dies, overstrikes on existing tokens, halfpennies struck on penny-sized planchets, etc.

If you fancy a good sit and read you can look up 'The Soho Mint & the Industrialization of Money' (Spink: Doty, R. 1998) or 'Matthew Boulton and the Soho Mint - Copper to Customer' (Brewin: Tungate, S. 2020); Tungate has an appendix with lists of weights and measures for all the coins and tokens described therein. The canonical reference is Charles Wilson Peck's 'English Copper, Tin and Bronze Coins in the British Museum 1558-1958' (first issued in 1964.) I don't have copies in my own library, sadly.

The 1806 issues proved rather more difficult to counterfeit thanks to the combination of the engrailed edge and the concave planchet, as well as Mr. Boulton's absolute insistence on maintaining strict tolerances for weight and diameter, but it's not beyond the realm of possibility that it's a fake. Soho was definitely turning a profit on genuine coins so there would have been a financial incentive for counterfeiters as well.

The cartwheel penny was counterfeited via mold casting as Herr Küchler's design had proved difficult to recreate by the forgers' die-sinkers. Lead casts were copper-washed. They were very soft and easily damaged in addition to being very mushy.

I've heard rumors that some were actually die-struck counterfeits using "recycled" well-worn genuine Soho penny planchets, but have never personally seen one.