All .30 lugers are not created equally when it comes to feeding- some will feed and shoot nearly any .30 luger round, others not.
Thanks to the guys who talk about reloading away the problem; but remember perhaps only 10% or fewer of the guys with a .30 luger will ever load for it!
The only "factory" ammo currently loaded is Fiocchi and PPU, try them- if one or both works -fine.
If not diddle with the mainspring after determining if it is a recoil problem or not. Old stock Winchester and Remington are hit and miss in my .30 lugers, some like it others don't- I would not pay a "fortune" for old stock ammo expecting it to be a solution.
Easiest way to do this is load one round, fire- if it locks open then the ammo is "strong" enough and the problem lies somewhere other than the mainspring.
Could be several things, from magazine to feed ramp to overall cartridge length, extractor, ejector, or something else.
Once you are tired of trying to fix it yourself, consider sending it to Lugerdoc for his evaluation.
JMHO.
