This is a factory FN 509 Compact 15-round extended magazine.

The FN 509 Compact handgun is the right size for concealment while still retaining the ability to carry 15 rounds. The FN 509C is compatible with the larger capacity 509 magazines, such as the 17 and 24-round factory mags.

Features:

• Durable steel construction
• Spend more time shooting with a 15-round capacity 
• Ribbed grip extension for better control
• High-vis orange follower
• Numbered, rear-facing witness holes
• Precise FN Herstal manufacturing

More info on the FN 509C:

The FN 509C is the newest EDC handgun from FN America. It comes standard with the FN low profile optics mounting system. This firearm is compatible with the larger capacity 509 magazines such as the 17 and 24 round mags. The gun includes two different size backstraps to ensure the best fit in a wide variety of hand sizes.

Pickup a spare FN 509C 15 round magazine at The Mag Shack.