Eric,
The cartridge counter was a product of two factors..
1. The need of the USA Army for a larger caliber than the 7.65 mm cartridge of the 1900 tests. DWM then developed the 9mm version.
2. The marketing need of DWM to get an edge over Colt who was clearly the favorite. The Powell indicating device was thought to give them something because it was developed by an American.
Hence the development of the Model 1902 with the Powell indicating device, AKA the Cartridge Counter.
Fifty were made because that is how many Model 1900 Test guns were exchanged with DWM for 50 Model 1902s with the Powell device. One was actually tested, and there are maybe 40 or so righteous specimens floating around.
Jan Still, in Imperial Lugers, page 210 and following discusses this gun and its history.
Goertz and Sturgess dissect the problem and write extensively about this experiment on page 260 and following of the revised (new) version. It was also discussed in the older version but I no longer own the older version so I canot give you an exact reference..
BTW, here is a link to a thread you started last year that provides a lot of detail on the magazine
http://forum.lugerforum.com/showthre...unter+magazine
John