ProMag SIGA21 20-Round 9mm Magazine for SIG P365/P365XL Steel

The ProMag SIGA21 extends magazine capacity to 20 rounds for SIG Sauer P365 and P365XL pistols, transforming these compact carry guns into higher-capacity platforms. This steel-constructed magazine addresses the capacity limitations of factory magazines while maintaining reliable feeding and function.

What Makes This Different

Unlike polymer alternatives, the SIGA21 features all-steel construction for enhanced durability under repeated use. The magazine extends below the grip frame, providing additional capacity without compromising the pistol's slim profile. Heat-treated steel components resist deformation during extended shooting sessions, while the precision-formed body ensures consistent cartridge presentation to the chamber.

Key Features

• 20-round capacity increases firepower by 67% over standard 12-round magazines
• Heat-treated steel body construction withstands high round counts
• Compatible with both SIG P365 and P365XL pistol frames
• Anti-tilt follower design prevents feeding malfunctions
• Removable floor plate allows complete disassembly for cleaning
• Extended baseplate provides improved grip purchase during reloads
• Standard magazine catch engagement works with factory controls

Range testing demonstrates reliable cycling with various 9mm ammunition weights from 115 to 147 grains. The extended magazine proves particularly valuable for competitive shooting disciplines where capacity matters, while also serving backup and training roles. The steel construction maintains spring tension over thousands of loading cycles, ensuring consistent performance in demanding applications.

Technical Specs

• Capacity: 20 rounds of 9mm Luger
• Construction: Heat-treated steel body and baseplate
• Compatibility: SIG Sauer P365 and P365XL pistols
• Overall length: Approximately 6.2 inches
• Width: 0.98 inches (matches pistol frame)
• Follower: Anti-tilt polymer design
• Spring: High-tensile steel coil spring
• Finish: Blued steel exterior

This magazine transforms the P365 platform into a higher-capacity option without sacrificing reliability or requiring frame modifications. Professional shooters and serious practitioners recognize the value of proven steel construction over lighter alternatives that may fail under stress.