The Luger selfloading pistol is one of the most iconic handguns ever designed, and has been very successful despite a rather archaic operating mechanism.
Georg Luger worked as an employee at Ludwig Loewe & Co, where Hugo Borchardt’s C93 pistol was manufactured. He took the toggle locking design somewhat clumsily used in the Borchardt and redesigned it to use a small leaf spring in the pistol’s grip instead of a clock-type spring in a separate housing. This allowed Luger to dramatically reduce the bulk of the gun, and make it much more practical as a military sidearm. The mechanism uses the same recoil action employed by other early autopistols, but instead of using a bolt to travel directly backwards the Luger used a toggle joint. This would lock solid when laying flat, but once the recoiling barrel cammed it slightly upwards at the joint it would open up to eject the spent casing and load a fresh one.
There are many available sources for excellent information on the Luger, so we will try to focus on some of the more esoteric varieties here.
A small handful of pictures of a prototype Japanese Luger. The characters on the left read “Tokyo Gas Electric Company Ltd” and on the right “Test Purpose Pistol”. It also has markings for “fire” and “safe” for the safety lever, and none of the typical proof marks. (Download gallery in high resolution)
US Patent #753,414 (G. Luger; Recoil Loading Small Arms; March 1, 1904)
This 5-part article details to effort of the Mauser company to produce new manufacture Luger pistols on 1970, with lots of very interesting details on production methods. Click to download in PDF format.