Hi all im new to the forum but have been building my own guns for a bit. I have 3 elite force m4s and just recently picked up a cfr and began messing with it. Ive installed the following to the gearbox. Raptor airsoft piston (was very heavy switched to shs lightweight) Raptor airsoft 13:1s (zci i think) these broke. (Switched to shs dsg) Lonex silent piston head 16 gauge wire Warfet mosfet. Just takeing the time to right this up for anyone interested in there guns since i love them because of there price and that they're easy to work on. Anyway a few things to look at upgradeing in the gearbox Tappet plate (kinda flimsy) Piston (does not sit straight in the gearbox and wiggles alot in the slides) Nozzle and cylinder head (basically zero compression here) Piston head (is extremely heavy) And finally add a mosfet to protect your microswitch. EDIT: UPGRADE BUSHING THEY ARE TRASH. 2K rounds thru dsg resulted in a bushing that looked like a pencil down a hallway.