Barrel tightnening?

[lemmonhead]

I recently purchased a number of guns from a shop that will be closing. All of the firearms were in need of some repair. In the group there were 4 Lugers and magazines. Two of the pistols look mostly complete and matching. The other two are mismatched and missing some parts.

One of the pistols, a 1917 ERFURT, has a barrel that is loose. I can remove the barrel by hand. If I tighten the barrel it will stop on time, if it is tightened anymore it will over time. Is there anyway to fix this? Peening or shimming? The barrel looks in fair to good condition.

I have removed and installed numerous rifle barrels, but Lugers are new to me.