Tightbore barrel, upgrade the hop unit to start with..... about £40 and £35 ish each. Then if you want more then get in the gearbox, high torque motor, stronger spring, mosfet, 11.1v LiPo....
I have one the same. I have a systema motor, and ultimate hop up with standard barrel. My local shop said it had the fastest rate of fire they had seen! Great basic gun!