The Glock 21 Gen5 MOS is a striker-fired semi-automatic pistol chambered in .45 ACP. The 4.61-inch barrel sits in an 8.03-inch overall package that weighs 1.81 lbs (27.68 oz) unloaded. Capacity is 13 rounds. The white dot front and white outline rear fixed sights are standard; the MOS slide accepts compatible red dot optics directly. The polymer frame includes interchangeable backstraps and ambidextrous controls. 
 

Key Specifications 

• Model: Glock 21 Gen5 MOS 
• Caliber: .45 ACP 
• Action Type: Striker-fired semi-automatic 
• Barrel Length: 4.61 inches 
• Capacity: 13 rounds 
• Weight: 1.81 lbs (27.68 oz) 
• Finish: Black polymer frame with matte black slide 
• Sights: Fixed white dot front sight & white outline rear sight 
   

Detailed Features 

1. Polymer Frame: Durable and light, absorbs some recoil and keeps total weight down for a full-size .45 ACP platform. 
2. Glock Marksman Barrel (GMB): Precision-cut rifled barrel for consistent accuracy. 
3. Safe Action System: Three passive safety mechanisms (trigger, firing pin, and drop safety) operate automatically without a manual safety lever. 
4. Ambidextrous Design: Reversible magazine catch and ambidextrous slide stop levers for left- and right-handed use.

The Glock 21 Gen5 MOS draws predictable feedback. Owners who buy a full-size .45 ACP Glock generally know what they're getting, and the Gen5 iteration earns broadly positive marks.

Accuracy is consistently called out as a strong point. The Glock Marksman Barrel improved on earlier Gen3/4 barrel designs, and owners report tight groupings at typical defensive and range distances. Reliability holds up across reports, with minimal malfunctions under regular use.

The .45 ACP caliber generates its own sub-discussions. Supporters cite stopping power as the primary argument; others point to 9mm's higher capacity and lower recoil for the same or smaller frame size. Neither position dominates in community threads.

The MOS optics system is appreciated by those who want a red dot, though some users mention that zeroing can take extra effort. Ergonomics are good for most hand sizes but the full-size .45 frame works against concealed carry, which is a common observation rather than a complaint. Weight and size are intentional trade-offs for the home defense and range shooting use cases where this pistol fits best. Aftermarket support for the G21 is deep across holsters, sights, and accessories.