I know there were a lot of WW I 9mm Lugers rebarrelled to .30 under post WW I restrictions.
Cramming a 9mm back into a .30 chamber is what seems unlikely to me.
Send pictures to
[email protected] and I will make a guess.
If not damaged by wrong ammo, the gun is worth a good many hundreds of bucks. There are a lot of different Luger variations and collector interest depends on a lot of fine details.