This is a Sig Sauer P320-M17 21-round extended magazine in 9mm.
Crafted from durable steel with steel internal springs, extended FDE polymer baseplates and a special anti-friction coating, these 21-round magazines are engineered to meet strict military specifications for performance and reliability.
Adopted by the US Army and trusted by police departments all over the world, the P320 delivers classic Sig Sauer quality in a polymer-frame pistol at a more affordable price than traditional Sig combat pistols. Its double-action-only cousin, the P250, is another popular, budget-friendly sidearm engineered for maximum performance and reliability.
These extended magazines offer enhanced grip area and improved capacity that's perfect for home defense, target shooting and more.