The G21 MOS provides a full-sized frame optimized for duty or competition use that is chambered in the venerable .45 ACP cartridge. The MOS series features an optic cut in the slide for use with Glock's MOS adapter plates that allow for universal compatibility with most aftermarket optics on the market. The Gen5 series is designed to FBI standards and comes with ambidextrous controls as well as a flat grip face for better ergonomics. A flared magwell also exclusive to the Gen5 series allows for easier reloads under pressure.