The Glock G21 Gen5 MOS is a striker-fired semi-automatic pistol in .45 ACP with a 4.61-inch barrel, 8.03-inch overall length, and 13+1 round capacity. The Gen5 updates include front slide serrations, a flared mag-well, and interchangeable backstraps. The MOS slide cut accepts compatible red dot sights without additional machining. The gas nitride-finished slide sits on a polymer frame, and the whole package weighs 29.81 oz (2.4 lbs) unloaded. 
 

Key Specifications 

• Model: G21 Gen5 MOS 
• Manufacturer: Glock 
• Action Type: Semi-Automatic (Safe Action) 
• Caliber: .45 ACP 
• Barrel Length: 4.61 inches 
• Overall Length: 8.03 inches 
• Capacity: 13+1 rounds 
• Weight: 29.81 oz (2.4 lbs) 
• Finish: Black (Gas Nitride) 
• Frame Material: Polymer Frame 
• Sights: Fixed Glock Sights 
• Optics Ready Cut: Yes 
   

Detailed Features 

1. Optics Ready Cut: The MOS slide accepts red dot sights directly, improving target acquisition without requiring a slide milling service. 
2. Front Slide Serrations: Improve grip on the slide during press-checks and chamber loading. 
3. Flared Mag-Well: Guides magazines in faster during high-stress reloads. 
4. Modular Design: Swappable backstraps allow grip size adjustment for different hand sizes.

The Glock G21 Gen5 MOS in .45 ACP gets discussed in ways that track closely with the broader Glock platform reputation. Reliability is the consistent anchor. Most owners report the G21 Gen5 running cleanly across a wide range of .45 ACP ammunition, which matters for a pistol used in defense or duty roles.

The MOS optics cut is a meaningful addition for anyone who wants to run a red dot, and the Gen5 ergonomic revisions generally land well with shooters who found earlier generations uncomfortable in the grip. The flared mag-well is a practical improvement.

Grip ergonomics are the most divided topic. The G21's larger frame works well for bigger hands; shooters with smaller hands occasionally note it feels oversized. This is a known trade-off for a full-size .45 ACP pistol.

Accuracy at typical defensive and range distances is broadly good, with shooters reporting consistent groupings after some trigger time. The 13-round capacity is well-regarded for a .45 ACP pistol. Some buyers wish for more options to expand capacity without adding grip extensions. Price is generally seen as fair for the Glock platform; some buyers compare it to alternatives at lower cost, but aftermarket support and the Glock ecosystem are factors that keep it competitive.