- R50 stands for Rifle - 50 Rounds in complementing contrast to the P50, the pistol version of the same platform. This carbine features a side-folding stock that rests nicely on either side of the grip when folded and a ½ x 28 threaded - 9.6 inch barrel. It does come with some utility sights that are adjustable for windage and elevation, however the R50 receiver offers over 7 inches of picatinny rail space up top for mounting just about any optic or accessory you like. 2 inches of rail space on the bottom is ideal for light and grip options. There’s a QD sling cup just above the magazine release for mounting a single point sling and the AR style charging handle offers smooth manipulation. Short Barreled Rifle Variant!