The R Series of combat assault rifles was used reliably following the discontinuation of the M Series in the early 21st century. The R series, produced by civilian manufacturer Stent Security Solutions, was made in many models and variations. The R91 assault rifle was issued in the United States National Guard during the urban pacification operations and combat.
The R91 is a full-auto assault rifle, effective from short to medium range. Its weight is 7 lb (loaded), it fires 5.56mm rounds in standard 24 round clips.