Finally found a better example of this cartridge.
I previously had an excavated example that I was pretty sure said 11 on it but was not 100% positive. It was recovered right outside Bunker Hill, WV in a Confederate camp from the American Civil War.
But this new one confirms it is indeed an 11. Also, there is an “M” marking. @jeanpierre is this a similar marking like the 4,7 and 12 on the shotshells? will it help date it? I think this has got to be probably about one of the very earliest metallic pinfire cartridges. He also made it in a 9mm: