This is a factory FN FNS 9mm 10-round magazine.

Here is more information on the FN FNS pistol:

The FNS™-9 offers the simplicity of double-action striker-fired operation with the option of a manual safety. The slide stop lever and magazine release are all fully ambidextrous for ease of operation with either hand from any firing position. Both the slide and barrel are stainless steel, and the checkered polymer frame has two interchangeable backstraps with lanyard eyelets. A MIL-STD-1913 mounting rail on the underside accepts tactical lights and lasers.