Semi-automatic versions of the M249 SAW (in use by the U.S. military since 1988), the FN 249S platforms feature chrome-lined, cold hammer-forged barrels, and make the most of potential accuracy by incorporating closed-bolt firing and intelligent stock designs. The primary differences between the two models within this series are the stock configurations and barrel lengths (which necessarily impact overall length and weight of each model). Both feed from magazines and linked ammunition belts, and are chambered in 5.56x45mm NATO.