Info needed on a German Luger

[Johnny Peppers]

If you now have a 7.65mm and a 9mm cartridge, a visual inspection will tell you everything you need to know about which caliber it is. If it is 7.65mm (.30 Luger), the bullet will go into the muzzle as shown in the first photograph. The second round is a 9mm, and it won't come close to going into the muzzle as shown in the second photograph.
The only round you could get into trouble with is the 9mmKurz also known as the .380 ACP. It won't quite chamber in the 7.65mm chamber, but it is so close that the bullet could be driven back in the case if one is chambered by letting the toggle assembly go rather than easing it down.

[Hoss]

Great info, thanks all. The 30 luger round did fit exactly as shown in that top picture. I went to the range this weekend so I decided to try firing it. It really was surprisingly accurate, and I didn't see any indications from the brass that I was using the wrong bullets. The only problem was that it misfed every single shot. I'm going to see if I can find a gunsmith familiar with Lugers to take a look at it. From what I've gathered about lugers, they are kind of picky about their magazines. So it could be that, or it could just be a weak spring. It might even be bad ammo since the box I had was of unknown age. I had the empty brass stovepipe most of the time, but I also had the next round get jammed instead of feeding and twice had the action not go all the way down (where I just needed to tap the top to get it to fire).