This is a .40 S&W factory extended 17-round magazine for Beretta Px4 Storm pistols, and Beretta Cx4 carbine (with Px4 Magazine well insert/release)
Beretta’s NATO-approved Px4 Storm features a unique rotating barrel assembly that helps mitigate recoil from the powerful .40 S&W cartridge, while keeping you on target for faster follow-ups.
These factory extended 17-round magazines give you a few extra rounds without adding too much height to the gun—making them the ideal choice for home defense, where you won’t always have a spare magazine handy. They’re also compatible with Px4 Compact pistols chambered in .40 S&W, Cx4 carbines chambered in .40 S&W and equipped with the Px4 magazine well insert/release.
Remember that extended magazines are still susceptible to wear and tear, so be sure to rotate them regularly.