Most jam-o-matic Lugers are just being fired with the wrong 9mm ammo. The Luger was designed to use 9mm+P level ammo and without it, many will fail to cycle correctly.
While its probably fair to say that if a Luger jams its because its being fired with the "wrong" ammo, the question is, what is the right ammo, and does the gun need work (and some DO) in order to reliably run on it.
The Luger was NOT designed to run on 9mm +p ammo. Period.
First off, the Luger was the first pistol made for the 9mm Parabellum. There was no such thing as 9mm +P in 1902, and the standards for the original ammo are well documented. (can't have a +p before you have a standard to add pressure to!
)
Georg Luger designed the 9mm Parabellum to fire a 124gr bullet at 1050fps from a 4" (100mm) barrel. This is the load adopted by the German Navy in 1906 (though the pistol chosen had a 6" barrel) and adopted by the German Army in 1908 (the 4" standard. and a bit later the 8" "Artillery" model).
Sometime before WW I, the load was changed to a 115gr bullet at 1150fps. This was the standard load used during both world wars.
That load level is listed in countless places, 115gr @1150fps (4' bbl). This is also the velocity listed for US 9mm Luger (before the +p "revolution")
Lugers have a reputation for being balky with US "standard" 9mm ammo. Personally, I think US 9mm Luger ammo from the "old days" was listed at a higher velocity than the ammo often delivered, and that's why so many Lugers became "jam-o-matics. If a Luger won't run on what the German Army fed them, it needs tuning.
Sadly, there is almost no one left who knows how, from personal experience, and so many Lugers are in the very valuable collector range that having them worked on so they will function reliably could detract from their value.
I would strongly advise AGAINST using any MODERN 9mm+p in a valuable Luger. The toggle system used is very efficient, and should handle a slight increase in pressure,
BUT not every part is as robust as the toggle lock, and we are talking about 75 year old (or more) steel and a single broken (numbered) part turns a $4k gun into a $2k gun (or less).
If you're willing to risk that kind of value loss, by all means, go ahead, its your gun. I don't run +P in my mismatched 1936 "shooter", but then it runs on standard 115gr & 124gr ball, provided the magazines are good. Lots of times, a balky Luger is a magazine problem, not an action problem. Not always, but often enough that its the first place to check if you have issues.