This an OEM Savage Arms BMAG .17 WSM 8-round magazine. 

The .17 WSM (Winchester Super Magnum) offers unparalleled performance in the rimfire arena, and this factory Savage Arms B.MAG magazine will have those rounds ready to go BANG every time.  Constructed from a high-quality polymer, it balances strength and weight perfectly. The rotary design and anti-tilt polymer follower ensure smooth feeding regardless of how quickly you’re shooting.  Thanks to its compact size, you can easily store a few in your go bag, hunting pack, or truck with ease.