Variant with a 24 inch (61 centimeters) barrel.

Variant with an 18 inch (46 centimeters) barrel. The RFB has a floating linkage bar between the sear and the hammer to prevent sloppy trigger pull. Unlike most weapons, the RFB's barrel is not free floating it is actually structurally integral to the weapon, serving as the weapon's 'spine' of sorts, where all other components of the rifle are attached to it. Casings drop from this chute to the left of the barrel. Spent cartridges remain inside the long ejection chute until one of three things happen: the weapon is tilted forward, the charging handle is operated or when another spent casing pushes the first one out. It uses a patented system that ejects cartridges forward of the shooter over the handguard of the rifle, with extraction accomplished by two extractors with two axis of rotation they can move from side to side to engage the casing, and then pivot upwards to eject the case. The RFB is a fully-ambidextrous bullpup rifle chambered for 7.62×51mm NATO and uses metric FN FAL box magazines that do not need to be rocked into place when loaded. The rifle started shipping to manufacturers in 2009, and it has since spawned a similar weapon, known as the RDB and a sub-variant of the RDB, the M43. The rifle was first shown off at the 2007 SHOT Show, and was declared to be made available in the 4th quarter of 2008 at the 2008 SHOT Show however, the release date for the weapon was pushed back to February 2009 due to manufacturing changes intended as preventative measures for gun control legislation. The rifle was developed by George Kellgren, a Swedish-born American designer best known for his work on the Intratec TEC-9, in 2003.

Fn fal grenade launcher