Luger caliber
 

How do you determine the current caliber I have a ww1 luger

two clues - look for the 8.xx mark under the barrel if it's a military luger - that would be for a 9mm
And try to slide a standard sized pencil into the barrel - it won't go in for a 7.65.

A photo of the barrel tip would help, too.

Both calibers use the same magazine.

Probably a 9mm as it is unit marked. Most likely a reblue, as the trigger and safety are blue instead of strawed. 1920 property marked. Dial calipers will tell you caliber, as well as the pencil test.

9mm no doubt~

We also have an item on this issue in our FAQ. Follow the link at the top of every forum page, and download the PDF document. It has a lot of good reference information including details on this subject.