The FN M249S is a semi-automatic rifle derived from the M249 Squad Automatic Weapon, chambered in 5.56x45mm NATO. The 18.5-inch cold hammer-forged barrel, steel receiver with hard-coat anodized finish, and gas piston action produce a 17.2-lb rifle that shoots from a 30-round magazine. 
 

Key Specifications 

• Model: M249S 
• Caliber: 5.56x45mm NATO 
• Action: Gas Piston (Semi-Automatic) 
• Capacity: 30 rounds 
• Barrel Length: 18.5 inches 
• Weight: 17.2 lbs. 
• Finish: Matte Black 
• Receiver Material: Steel 
• Receiver Finish: Hard Coat Anodized 
   

Detailed Features 

 
The gas piston system cycles reliably with minimal maintenance intervals, which makes sense given the M249 platform's military heritage. The cold hammer-forged barrel is matched with a removable heat shield that keeps hands clear of barrel heat during extended firing. Adjustable iron sights allow distance adjustment without tools. 
 
A cross-bolt safety prevents accidental discharge. The steel receiver with hard-coat anodized finish is built for durability rather than weight savings — this is not a light carry rifle at 17.2 lbs. It accepts both standard STANAG magazines and disintegrating-link belts (belt-feed requires the appropriate feed tray, as shipped from factory in semi-auto configuration the M249S ships as a magazine-fed rifle). 
 
The 18.5-inch barrel extracts more velocity from 5.56 than carbine-length barrels, which is relevant for longer-range work.

The FN M249S draws enthusiasts who want the aesthetic and heritage of the M249 platform in a semi-auto, legal civilian configuration. Owners consistently praise the build quality — the steel receiver and FN construction are as solid as you'd expect. Accuracy at medium range gets good marks.

Weight is the defining practical consideration. At 17.2 lbs, the M249S is significantly heavier than any AR-15 or similar platform. That's the physics of the design, and most buyers know what they're getting into. Price is the other barrier — the M249S is one of the more expensive 5.56 semi-auto rifles on the market. Aftermarket accessories sized for the M249 platform are less common than AR-pattern options, which limits customization.