Agree

I would have thought with all that information on the gun - proof, year etc etc - and even if you don't cerosafe the chamber, you must know what the bore is, you can have a damn good guess at the calibre.

Have a look in the Mauser books.

Secondly, that gun looks is fairly good condition with all it's bits - and possibly even matching serial numbers.

It would be a shame to take it apart as so few originals are left. If you want a custom barrel, buy an old Mauser 98, plenty of those around.

Just my HO.