This is the ProMag FN P90, PS90 5.7x28mm 50-round magazine. 

Save some money for more ammo by ordering a few of these high-quality aftermarket FN P90 magazines by ProMag! 

Thanks to the impact-resistant polymer body, this magazine remains lightweight even when fully loaded with all 50 rounds. The heat-treated music wire spring and injection-molded polymer follower work together to feed your P90/PS90 flawlessly. 

You’ll find round count indicators on the rear of the translucent body, allowing you to track your remaining capacity easily. Whether you’re gearing up for a trip to the range or reserving your P90 for home defense, these magazines will fill the role nicely.

At this price, you might as well grab a few!