Hi Paul, welcome to the Luger Forum.
Your 1940, Code 42 is indeed a 9mm. The 8,81 refers to the distance across the lands in millimeters or 8.81 mm.
It was fairly common for GIs returning from Europe to have their war trophy "enhanced" by getting them chrome plated. Unfortunately, it ruined the pistol as far as it's collectability is concerned. <img border="0" title="" alt="[Frown]" src="frown.gif" />