Thing runs on k25 and an upside down rscb. Top barrel is faux and only for looks. Barrel spacer in the front is made of 1/4" polycarbonate. FPS unknown as I don't own a chrony, but if I had to guess, between 150-170. It is hitting consistent flat shots of 85-90 feet. First proper mod in a hot minute, very happy with how it turned out.