I went through "Mauser Pistolen" (Weaver, Speed & Schmid, 2008) again...... step 10 in 1938 factory assembling instruction of 6,35/7,65 was "After bluing, the barrel is emeried [smoothed with emery cloth] at the cartridge feed ramp, chamber and muzzle" (page 201).
I looked up the meaning of "emery cloth" on the web ..... being a type of "sand paper".
Probably similar step was applied to other type of Mauser pistolen.
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