The Glock G21 G5 MOS is a full-size .45 ACP pistol with an optics-ready slide and a 13+1 round capacity. Three magazines are included. The Gen 5 frame uses a grey polymer with front and rear slide serrations, a flared mag-well, and Glock's Modular Optics System cut so you can mount a red dot without an adapter plate. 
 

Key Specifications 

• Model: G21 G5 MOS 
• Caliber: .45 ACP 
• Barrel Length: 4.61 inches 
• Overall Length: 8.03 inches 
• Capacity: 13+1 rounds (3 magazines included) 
• Weight: 29.81 oz. 
• Finish: Gas Nitride (Black) 
• Frame Material: Polymer Frame 
• Stock/Grips Color: Grey Frame 
• Sights Type: Fixed Glock Sights with an Optics Ready Cut 
• Additional Features: 
  • Front Slide Serrations for grip during slide manipulation. 
  • Flared Mag-Well for faster reloads. 
  • Modular Optics System for direct optic attachment. 
     

Detailed Features 

The Safe Action trigger delivers a consistent pull from first round to last. There is no external manual safety; the three internal safeties disengage only when the trigger is pressed correctly. The polymer frame keeps weight down at 29.81 oz. unloaded while still holding up to hard use. 
 
Fixed Glock sights handle most conditions well, and the MOS cut lets shooters drop in a red dot for faster target acquisition. The flared mag-well makes reloads noticeably quicker under pressure. 
 

Target Audience 

This pistol suits experienced shooters who want a proven .45 ACP platform with modern optics compatibility. The ambidextrous controls make it usable for both right- and left-handed shooters. 
 

Usage Scenarios 

• Home Defense: 13+1 rounds of .45 ACP and a consistent trigger make it a capable defensive pistol. 
• Competitive Shooting: The MOS cut and flared mag-well support fast, accurate work in action competitions. 
• Training: The straightforward Safe Action system and manageable controls work well for range sessions at any experience level.

Users of the Glock G21 Gen 5 MOS generally rate it highly, though feedback splits along a few consistent lines.

On the positive side, reliability gets mentioned most often. The G21 cycles reliably with a wide range of .45 ACP loads, and the Gen 5 ergonomics (smoother grip texture, no finger grooves) are widely preferred over earlier generations. The MOS cut is a genuine draw for owners who run red dots; mounting is straightforward without an adapter. The 13-round capacity is appreciated for a .45 ACP pistol of this size.

The main criticisms center on weight and recoil. At 29.81 oz. unloaded, it is on the heavier side among polymer-framed pistols, which affects all-day carry comfort. Some shooters find .45 ACP recoil in the G21 more noticeable than they expected, though most adapt quickly. There is also occasional discussion about aftermarket support being narrower than what is available for the 9mm Glock lineup.

Overall, owners tend to view it as a solid, no-surprises .45 ACP handgun that handles modern features well.