Thanks for getting back to me.

Unfortunately, I can't find a .XX number on my rifle anywhere.

The serial number of the rifle appears to be 5954. This number features on the right side of the breech and in front of the recoil lug on the receiver. It's also stamped onto the base of the bolt handle, inside the magazine assembly, and on the underside of the magazine follower. The last two digits also appear on the bolt head and parts of the magazine assembly.

The only other numerals that I can see are a +1 and a -1 that appear on the underside of the barreled action (one on the barrel and one on the receiver). The magazine also has the letter K on it in several places while the rear of the receiver is also stamped with the letter B.

On the subject of proof marks I have to confess I know very little however, would it be normal for an Austrian proof house of this period to inscribe a rifle with the words "Nitro Proved"? That seems odd to me as does the symbol with an arm and scimitar over the letters "NP".