Have a rifle that came without caliber markings.
Determined bore was .375"

Could see that there was a belt in the chamber so tried a .375 H&H.
Much too long so time for a chamber cast.

What I found was a belted mag with:

.532" belt
2.50" Case Length (Approx.)
.406" Neck Diameter
.494" Shoulder Diameter
.350" Neck length (Approx.)

I can take additional measurements if needed.

It appears to be a shortened, improved H&H.
Searching Cartridges of the World and the internet I cannot find a match.

Is this some obscure cartridge? Known wildcat? Or a one off wildcat?

Any help appreciated!