Apart from the standard 10 round internal magazine of the Model 1908 and its derivatives there are two known detachable magazines.

The first is the German FSK15 and its 30 round detachable drum magazine and the Swiss Model 1917 and its 12 round detachable magazine.

The FSK15 has a drum magazine containing 30 rounds of 7X57mm Mauser.  A folding arm extends and when rotated releases tension on the internal spring to allow loading.

The Swiss Model 1917 is a more traditional straight magazine inserted from underneath.  It holds 12 rounds of GP11 or as we know it, 7.5 x 55 Swiss.