Hi Burney,
I believe this is most likely a modern DENIX reproduction (simulacrum) of a .30-06 Springfield cartridge, rather than an old toy gun bullet
The one-piece cast construction is typical of DENIX inert display replicas and the overall dimensions and shape appear to match their reproduction .30-06 rounds which is made for their replica firearms such as the M1 Garand and Browning Automatic Rifle (BAR) , Although the item has an aged appearance, this is more likely due to surface patina or wear.
I’ve attached an image and a link which appears to match your example very closely.
Best regards,
Matthew
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