Rail Mounted Fixed Loop (RMFL)Blue Force Gear Rail Mounted Fixed Loop (RMFL) The Rail Mounted Fixed Loop (RMFL) allows a quiet, secure sling mounting loop to railed fore ends. Machined from aluminium and hard coat anodized, the RMFL provides a solid and silent sling loop on MilSpec 1913 hand guard rails (may require minor fitting on others). This Rail Mounted Fixed Loop is issued with the USMC M27 Infantry Automatic Rifle, and is also approved for use with the M4, M4A1, and M16A4.