I spent more than $650 to upgrade the MK18. I changed anything to best parts. I changed a high performance custom motor and changed anything in gear box. All are replaced with the best and hardest components. This gun can support least M150 spring. Until to now，this gun has more than 460-500 FPS with 0.25 BBs. and 50 RPS. （Ask me for video） Items include： 1: rifle 2: 4 mags 3: 1 more Magpul Stock 4: AceTech Predator AT2000 Tracer Unit w/ VFC QD Mock Suppressor & Steel Flash Hider 5: Magpul USA AFG2 AFG II Angled Fore-Grip 2 Rail-Mounted Forward Grip 6: Madbull Airsoft Ultimate 6.01mm 7075 Aircraft Aluminum Tightbore Barrel ... $25 ship fee