Posting on behalf of a friend.
My friend sent me this photo.
Left- .22LR shotshell
Right- nailgun blank
This mystery cartridge bears an ICI headstamp and appears to contain lead shot when rattled near the ear. It also appears to be .25 calibre
I’m clueless as to what this is. The only .25 calibre rimfire round I know is the .25 Stevens Rimfire but I can’t find any reference to shotshells being produced in this calibre.