Antre du Dingo Dingchavez review the SAT Variable Velocity Device which allows you to adjust the power of your AEG without any need for a spring change... "There's no QC spring system on your AEG? You're fed up with having to swap for a lighter spring every time you go to CQB? Here is a solution to your problem: the Variable Velocity Device. A piston and a piston head that can be adjusted on the fly!"