The TKO - 4 round, short dart, inline clip, Nerf Rival Knockout

CORRECTION: The muzzle piece does not just fit onto a stock Knockout. the orange piece of plastic beneath the barrel on the Knockout gets in the way. My bad there! Here's a brief overview of my 4 round inline clip Knockout, which I'm calling a "TKO". I am using the stock Knockout spring and in this 4 shot configuration I am getting an average of 125fps. Materials used in my build: one 8 1/2 inch length of polycarbonate tubing (5/8" ID, 3/4" OD, 1/16" Wall) one 3 1/8 inch length of polycarbonate tubing (1/2" ID x 5/8" OD x 1/16" Wall) one M3 brass insert one M3x30mm socket head bolt two 014 o-rings, 70A Durometer (1/2" ID, 5/8" OD, 1/16" Width) Thingiverse link for 3D printed parts: https://www.thingiverse.com/thing:434...