The FN 15 rifle series is based on FN's semi-automatic, direct impingement platform for the 5.56x45mm, .223 Remington, and .300 AAC Blackout (7.62x35mm) cartridges, and offers something for everyone, whether the application is tactical, collector, or target/competition. At the core of each FN 15 stocked by EuroOptic is a hard-anodized aluminum, flat-top receiver, featuring a full-length Midwest Rail System with M-LOK technology (unless indicated otherwise in the individual product description) for enhanced rigidity and accuracy potential. Barrel length (cold hammer-forged, chrome-lined) varies from 10.5" to 18", and replacement barrels are available.