Walther original grip extension for your p99c, allows use of full size 15rd/16rd magazines.These can also be used on your normal sized p99/sw99 with the 20rd mags.

Caliber: Grip Extension
Capacity: P99C
Model: P99C
Material: Polymer

Magazine Restrictions:

The following states have magazine restrictions. Your order will not ship to those states if in violation of these laws and will be subject to cancellation and a 15% restocking fee.

California - Limited to 10-round capacity.
Connecticut - Limited to 10-round capacity.
Colorado - Limited to a 15-round capacity.
Delaware - Limited to 17-round capacity.
Hawaii - Handguns limited to 10-round capacity
Illinois (Cook Co, Aurora, Highland Park) - Pistol mags are limited to 10 rounds.
Massachusetts - Limited to 10-round capacity.
Maryland - Limited to 10-round capacity.
New Jersey - Limited to 10-round capacity.
New York - Limited to 10-round capacity.
Road Island - Limited to 10-round capacity.
Vermont - Handguns limited to 15-round capacity, Rifles limited to 10-round capacity.
Washington DC - Limited to 10-round capacity.
Washington - Limited to 10-round capacity.