Russian 5 Kopek 1763 Overstrike

So this looks like a well-lived overstrike over a 1762 10 kopek piece, which isn't that unusual (although most of the overstrikes I've seen pictures of were from the Yekaterinburg mint, not St. Pete's). Being thinner (only ~2.6 mm) and wider (43.5 mm) than the typical 5 kopek monsters is probably reasonable for an overstrike. But the metal bothers me-- the coin is much paler in color and lighter in mass (39.3 g) than the other 5 kopeks I've seen. Can anyone explain what's up? I apologize for the suboptimal images; I need to get some new batteries. Thanks!


You can see a couple of the 10 kopek's stars in the lower left quadrant.




Some highlights outlined.