Note that I am selling TWO of these, both of which are the same. Modified KRYTAC Version 2 Gearbox with M-125 spring installed as opposed to default M-120. M-125 spring increases FPS from 330-340 to 360-370 with .25g bb’s. Will fit inside most air soft guns with V2 gearboxes. Rate of fire, 20-25 rounds per second with 11.1v Lipo.