This 1803 half cent was subjected to XRF analysis. There were two primary elements detected, Lead (78.5%) and copper (18.%) with traces of antimony and tin. This alloy also corresponds with a heavier (denser) example weighing 6.55 grams (genuine half cents of this type weighed 5.44 grams when new).  The edge also appears to have traces of a seam that were worked on and prepared a little to hide the seam. In contrast, this doesn't seem to match the characteristics of a cast counterfeit as these would typically have a more diverse white metal alloy and not be purely tin as in this example.

It is unclear why a non-rare (or low mintage) date was made into a probably electrotype, but maybe this was a test piece or someone just needed to fill this hole in their collection. Either way, this example may be unique for the denomination and date.