Anyone know what this is??

[Tex Critter]

Few weeks ago was up in Pet doing trg and ranges. I found a strange looking cartridge that was rimmed, straight walled like a .303 Brit with a serrated case mouth. Can't remember the head stamp markings though. It looked similar to this:

 

[Winnipeg Toymaker]

fire formed .303 British to make .410 shot casings for the Ishy conversions? flare? blank?

 

[tootall]

Show us the headstamp.
Although from the serrated mouth, I'm wondering if it is a primer for large artillery

 

[Ganderite]

Blank?

 

[dragoon7214]

It's an M82 or DM191 primer for 155mm arty. The headstamp will tell you which one it is.

 

[Al-Sway]

I won't dispute the call on 155 arty primer.
If it were a .303 blank, it would still have a shoulder and the case mouth would be rose crimped. Not as shown in the photo.