The Remington GPC (or Remington R4) introduced in 2010 was a AR-15 derivative with an extruded upper receiver acting as a barrel cooling jacket mounted with STANAG rails. A derivative product called the Modular Gas Piston Carbine was being offered to the US Army for its Aborted Improved M4A1 Program . It features a Ferritic Nitrocarburized (FNC) coating, 10.5 inch or 14.5 inch barrel offerings with a six groove 1:7 right hand twist. The hand guard is an eight-sided ventilated free floating unit with monolithic Mil-Std-1913 rail on the upper portion and user configurable rail sections that can be added on the other seven sides. The Remington R4 would become in 2012 the prototype for a line of Ar15 based carbines produced under the Remington brand for Defense and Civilian applications. this series consists of the R4; a Direct impingement operated M4/M4A1/M16A4 clones, and R5 or Remington Gas Piston; the most direct production version of the GPC. both series use off the Shelf Furniture including M4 style teliscopic stocks, pistol grips and in the case of the R4 traditional M16A2 or M4 style round hand guards. however Variants of the R4 and the stock R5 are offered with updated versions of the GPC's Forearm and use Magpul stocks and Ergo pistol grips.