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I'd bet it IS .30-06, just... manufactured out of spec. If it's foreign military surplus, I'd not be surprised at all to see variances like that. Looking at the extraction groove, I'd guess the Greek stuff was "modified" to allow a heavier, more difficult to break extractor, as well as moving the walls of the cartridge forward a bit to deal with out of spec feed ramps and the like.

Not sure I'd want to shoot that in a Garand, though; not because of the weird-looking extraction groove, but because it IS foreign surplus, and I don't know their quality control, the powder burn rate, or how much force it's going to put on the operating rod of the rifle, as compared to US military ammo. I doubt I'd have any qualms shooting it in a quality bolt-action, though, especially not one built off a Mauser-style action.