Yes, I see it now: 7X57 MM

There are also 'vise marks' on the receiver and barrel.

Likely, the barrel was taken off, one thread machined off the breech, and the barrel re-bored & re-chambered for 7mm Mauser. (This would be the safe way to alter the barrel/chamber).

Altered photo shows 'vise marks' (orange) and gap in wood channel from barrel being moved-back (green).

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