Punt gun

[Fronteria]

If that is a 3.5" 4 bore case, the punt gun case must be over 9" I wonder what breech action was? Screw probably

Hi. Tomcat.
The cartridge is a touch over 10" I don't know what bore the breech loader that used this cartridge was but it would have made your ears ring when it was fired.
I think you are correct about it being used in a screw breech punt gun.