M4-22 PRO TS2O Red Dot Sight with Riser, Flip up Sights, 25 + 1, 16" Barrel The M4-22 PRO TS2O is a premium .22 caIiber semi-automatic tactical rimfire rifle. It features an aluminum upper and lower receiver, a Red Dot Sight with Riser, and is compatible with most AR15 stocks, handguards, and sights. With its true M4 look, feel, and controls, it's ideal for training or backyard plinking.