[Zfurlong]

first and foremost you will need to set a budget as prices can widely vary. as for upgrades, start with your hop up. after your hop, you will then need to look at airseal.

most expensive:
shs or siege speed gears, torque motor, silver wiring deans connectors, metal tooth piston, full cylinder, sector gear delayer chip (allows just that much more time for feeding and helps prevent blank firing and double feeding), the appropriate spring (usual go to is an m100-m120 depending on brand), correct the aoe on the piston, double oring piston head, double oring cylinder head, double oring nosle (sorry a certain key on my keyboard is busted).

have a proper tech put it all together and have them shim the gearbox properly while they are at it. and if its not already done, have the tech install a mosfet as well. this all can run you upwards of a grand or more in cost, but as mentioned above, start with the hop as this will be your most noticable performance increase. (i have a stock echo1 ak with nothing done to it other than an rhop promy, gun is 12 years old, all stock parts save the hop, never taken apart, never cleaned. shoots 247 on .3 it out ranges anything ive put it up against, with tighter groupings than anything ive put it up against. and yes ive put it up against upgraded polarstars as well). i run it on 7.4 lipos and while trigger response could be better, she performs beautifully as she is.

any further questions, feel free to pm me