Kel-Tec R50, Semi-automatic Rifle, 5.7X28MM, 16 Barrel, Threaded 1/2x28, Matte Finish, Black, Folding Stock, 50 Rounds, 2 Magazines R50BLK The R50 is the rifle version of Keltec's P50. The rifle has a side folding stock, attached to the bottom of the pistol grip, that can pivot left or right and a 16" threaded barrel.