While most major pistols made before the 1930s had some type of shoulder stock available as an option, the Luger had much more variety of stocks than most others. In addition to the several types of wooden stocks made on military contract, there were also several commercial types of folding stocks made. One of these was the Benke-Thiemann, originally designed by Hungarian Josef von Benke and improved by Georg Thiemann.
This stock was made of sheet metal stampings, and attached by replacing the grip panels of a Luger pistol. When folded, the stock added remarkably little size to the gun, and could still be fired, albeit with a somewhat awkward grip. This was done by cleverly designing the stock to consist of two layers of material which overlaid each other when folded, but then could be held end to end when extended, providing a stock of surprisingly usable length and sturdiness. A single spring-loaded latch was employed to lock the stock in both the folded and extended position.
Ultimately the stock failed to be a commercial success, probably due to costs and worldwide economics in the 1920s when it was developed. Only a few hundred were made, although the serial numbers all have leading zeroes to accommodate an anticipated production in the tens of thousands.
Stocked FN 1903: https://www.full30.com/video/771479fec22105b78bf09b1509d4de0e
Colt 1851 w/ Canteen Stock: https://www.full30.com/video/bbd8b48a24f0dd9f730d9a3406b84476
Fiala 1920 Combination Gun: https://www.full30.com/video/5012cb78a4b5601d064a9ea5a9d82c20
Mauser 712 Schnellfeuer: https://www.full30.com/video/0795387128863461640faffd4bb8a3ad
Shansei .45ACP Broomhandle Mauser: https://www.full30.com/video/16fa17b1475706b987571591c11c81c3
Luger 1902 Carbine: https://www.full30.com/video/972a370125b4407647e94601ca4699cf