Any idea what this isn’t?

[cdet69]

239101

[maxreloader]

Rimfire garden-gun cartridge? Maybe European. Have seen similar around at cartridge collector shows.

[Bazoo]

Cartridges of the world lists several small shotshells like that. The older 5th edition does atleast. If you give the dimensions I'll see about looking for you.

[edp2k]

Possibly a shell for a 9mm shotgun.

[salpal48]

Several 9mm Shot shell were for cane guns. they were simpler to make tan center fire

[Earlwb]

I agree a small rimfire shotgun shell for a parlor/garden gun. Back in the late 1800's to early 1900's it was popular for the European rich to have parlor or garden guns and gun ranges. They used small shotguns for that purpose. a 9mm shotgun was the one. There were cheap ones and good expensive ones made. it wasn't very popular in America though. Not all that many of the things made it across the Atlantic. Anyway there were quite a few companies that made the ammunition for them.

ref http://www.ammo-one.com/9MM-SHOTGUN-SHELL.html

https://en.wikipedia.org/wiki/Garden_guns

[turtlezx]

think winchester made a 9mm garden gun

[Traffer]

Yup my first thought was a 9 mm flobert. I don't think it could be anything else.