NitroX, thank you, yes. 9.5X57.

Rothhammer, thank you. Yes, I remember taking down the bolt that way in my M1903 (made in Germany (as stamped on the receiver) in 1939 (based on the proof mark).

The problem with pressing down on the head of the bolt is that is where the diopter sight is. There is nowhere to press. I will post a photo tonight.

The receiver is NOT stamped "Made in Austria", so before 1924. Also, stamped "Oesterr. WaffenFabr. -Ges Steyr", so before 1926.

No proof mark of any type visible. I had expected to see the NPV stamp from Vienna, or perhaps the NPF from Ferlach, but neither was there. Just the circle G (?), Circle T ("Tiegelgussstahl"), and the "0" on barrel and receiver. I will post a photo tonight.

Thank you all.