This Sig Sauer Magazine is a Factory Original Replacement Part, manufactured to the same specifications and tolerances using the same materials as the OEM Magazine that came with the pistol, guaranteeing optimal fit and reliable operation. When it comes to semi-automatic firearms, the ammunition feeding device often determines if, and how well, the gun functions. Therefore, whether for use as a backup mag for your concealed carry pistol, or simply to spend a little more time shooting and a little less time reloading on the next trip to the range, keeping a few spare factory magazines handy is never a bad idea.