Thank you Kos-Mos. I have a +-500$ budget. I heard that a stock hop up wont hold +500fps? And I don't know if you could tell me brands names because this is one of the things that I find difficult to choose. Let's say that "OK" made a tune up kit for 500fps with cylinder/piston/spring guide and spring. Can I just swap the spring that come with it with a stronger one? Thank you
