Unknown 25mm replica?

Before I put this into the ammo bin of obscurity, does anyone know if it is a replica of an actual round ?

The case is brass and the bullet is bronze, as it is very very heavy for it’s size I guess it’s been machined from solid stock. .303 for comparison.

Where the primer should be is a steel insert.
O/A length is 138mm
Bullet dia is 25mm
Case length is 90mm
Case mouth is 25.75mm
Neck dia is 26.31mm
Case dia is 32.40mm
Rim dia 32.40