30mm projectile ID help


Can anyone identify the 30mm projectile shown below? It is approximately 68mm in length and it weighs 324 grams. It appears to be solid steel with a copper rotating band. There are no markings at all anywhere on the projectile.

My guess is that it is some type of proof projectile for a 30x113B cartridge but that is pure speculation. If anyone has a definitive ID it would be appreciated!