Ted,
There is no ammunition available which truly replicates the original 9x19 Parabellum round. Modern 9mm Para. ammunition spec. has an overall length slightly shorter than the original. From 1908 to 1914 the bullet was in the shape of a truncated-cone; it was changed to an ogival shape. Bullet weights varied between the range of 70-150 gr.
The practical answer to your question is, that there is modern ammunition, which functionally more-or-less approximates the original ammunition. It seems that overall length and bullet ogive are the crucial to ammunition functioining properly in a Luger; bullet weight is somewhat less of a consideration. It is necessary to perform actual tests to determine what ammunition will function with your Luger
In my experience, Winchester bulk-pack from Wal-Mart, Sellier & Bellot, CCI Blazer, and Federal American Eagle all work consistently and completely reliably in the Lugers I shoot. All these are 115 gr. FMJ.
Remington UMC, Speer Lawman, and all commercial reloads I have tried, consistently and frustratingly fail to operate a Luger properly.
An additional consideration is the magazine. Feed angle is crucial to proper Luger operation. The original Luger pistol was designed for a bottle-necked 7.65mm round; the 9x19 Parabellum cartridge is essentially a necked-up, straight-sided version of this case. This is why 9mm and 7.65mm operate the same firearm: the lower case and head diameter, and length are identical. It is easy to picture why a truncated-cone bullet would feed well in a system which was initially designed for a smaller-diameter bullet entry, and why an ogival bullet might not.
Original crimped-steel Luger magazines, which are 60 to 100 years old, very often have feed lips which are worn or "sprung" and no longer set the next round at the proper angle to feed properly. This exacerbates the feed problem of a cartridge which is the wrong length, or has a bullet with too wide an ogive. Magazine springs can be too weak to retain the bullet firmly in its proper orientation. Extruded-steel magazines, manufactured by Heinel beginning in the late '30s, are inherently more stable, and have been subject to much less use wear.
Modern magazines (particularly those by Mec-Gar) are the way to go for shooting Lugers. One correspondent to these Forums asserts that overall cartridge length is the overriding factor in proper function, and notes that these magazine's internal length is slightly less than the originals, thereby permitting the shorter, modern 9mm Parabellum round to function properly.
--Dwight
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