Early in the production of the C96 Mauser, the company tried a variety of different configurations of the pistol, to see what would be popular and sell well. Most of these were abandoned by about 1902, when the design was more or less standardized to the version were are familiar with today. One of the early experiments was with a 20-round fixed magazine, or which 188 were made. This was fed using two 10-round stripper clips, and that seems to have been the biggest problem with it. According to some folks who have used these, the magazines is quite difficult to fully load, making the 10-shot version rather more practical.
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