Re: I blame the empire!
Hah. You'd think, but how heavy was a french 36 pounder cannon ball? The answer is 39 pounds, 11 and a half ounces. In generally accepted English pounds before standardisation in 1824 of course. No idea what that is in modern (1876) Imperial, but I'd assume that it's going to be different.
Muskets were actually hand manufactured everywhere to different sets of measurements and it was reasonably common to get your own set of moulds to pour lead into to make bullets for your weapon that would fit. ;)