The Sig Sauer M18 is a compact, striker-fired 9mm pistol on the P320 platform. Barrel length is 3.9 inches, and a Romeo reflex optic comes pre-installed on the slide. The frame is black polymer, the sights are SIGLITE-style for low light, and it feeds from a 17-round magazine for a 17+1 capacity. This "Off Duty" package pairs the M18 with the optic already mounted, giving it a day-and-low-light setup out of the box. 
 

Key Specifications 

• Brand: Sig Sauer 
• Model: M18 
• Caliber: 9mm 
• Action: Semi Auto 
• Capacity: 17+1 
• Barrel Length: 3.9 inches 
• Color: Black 
   

Detailed Features 

• Romeo reflex optic pre-installed on the slide for faster sight acquisition 
• Factory SIGLITE-style night sights for shooting in low light 
• Black polymer frame on the P320 architecture 
• 17-round magazine included, for a 17+1 capacity 
• 3.9-inch barrel, shorter than the full-size M17 in the same family 
• Built for everyday handling and everyday carry use

The M18 gets picked over the full-size M17 by owners who want a similar feature set in a more concealable package, and the 3.9-inch barrel is generally described as a good middle ground between a compact carry gun and a full-size duty pistol. The factory night sights are a consistent point of praise since they save the cost and hassle of an aftermarket install.

The pre-installed optic is convenient for owners who want to start training with a red dot right away, though a few mention that a higher-end optic can be a worthwhile upgrade down the line. Recoil control and follow-up shot speed get good marks thanks to the grip module shared with the rest of the P320 line.

Value opinions on the M18 are generally positive given how much comes factory-installed, and the shared parts and magazine compatibility across the P320 family means spare mags and holsters are easy to source. Some owners do note the trigger feels heavier out of the box than they expected until it's had a break-in period.