The Remington GPC 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 R5 is essentially a gas-piston derivative of the previous Remington R4, itself a clone of the AR-15/M16/M4 series., The standard R5 comes with a Magpul stock and an Ergo rifle grip.