Sig Sauer P320/M17/M18 9mm Luger 21-Round Extended Magazine - Black/Coyote Steel

Running low on rounds mid-string at the range or in a defensive scenario isn't an option. The Sig Sauer P320/M17/M18 9mm Luger 21-round extended magazine lets you shoot longer between reloads while maintaining the same rock-solid reliability you get from factory Sig magazines. Built to the same exacting standards as the magazine that came with your pistol, this steel-bodied mag is engineered for shooters who demand confidence in their equipment—whether you're training hard or carrying serious capability.

This 21-round extended magazine works seamlessly with P320 full-size platforms, including the M17 and M18 variants. The high-lubricity finish ensures smooth feeding cycle after cycle, while the high-tensile spring delivers unmatched reliability and long service life. A removable base plate makes field maintenance straightforward, and witness holes marked in 5-round increments let you see exactly how many rounds remain at a glance—no guessing during competition or training.

The steel construction and durable polymer follower are built to handle serious use. If you're running a P320 and want the flexibility to keep more rounds in the mag tube, this extended option gives you factory-grade performance without compromise.

Key Features

• 21-round capacity for extended shooting between reloads
• Factory Sig Sauer reliability and quality standards
• High-lubricity finish for smooth, consistent feeding
• High-tensile spring for durability and service life
• Witness holes in 5-round increments for quick round count
• Removable base plate for easy cleaning and maintenance
• Complete steel body with durable polymer follower

Specifications

Frequently Asked Questions

Will this 21-round magazine work with my P320 M17 or M18?

Yes. This extended magazine is compatible with P320 full-size platforms, including the M17 and M18 variants chambered in 9mm Luger.

Is this a factory Sig Sauer magazine or an aftermarket clone?

This is a factory Sig Sauer magazine built to the same reliability and quality standards as the magazine that shipped with your pistol.

Can I remove the base plate for cleaning?

Yes. The base plate is removable, making field maintenance and cleaning straightforward.

How do I know how many rounds are loaded?

The magazine features witness holes marked in 5-round increments along the side, allowing you to see the remaining round count at a glance.