Forget the chronology I started out with for shell lengths growing in the late 1890s. I was working in the beginnings of smokeless powder shotshells.

Check this out from the 1880 Union Metallic Cartridge Co. catalogue --

http://img.photobucket.com/albums/v3...psf1b8b662.png

I wonder if that Cashmore didn't have its chambers lengthened sometime after it was went through proof. The mark for longer than 3" chambers was a 12 in a diamond over LC. 3" or less was 12 over C.