Projectile id please

Went metal detecting today, found three of these bullets, they were found in South Australia in a gun range that was active in the 50s and 60s. Would anyone be able to tell me what caliber they are and form what bullet shell?

The dimensions are 12mm by 29mm but it has been fires so would have been longer. I compared it to my .50 BMG shell and it’s slightly too small
Cheers Hamish

It would be a .450/577 Martini projectile. These are relatively old compared to the dates you mention, maybe someone having a play on the range with an oldy.