Hello airsoft society. I just bought a S&T PP-19 Bizon the other day and I originally wanted to simply do some rewiring, connect it to deans and use it as a CQC gun. Well turns out it shoots over 420FPS! So I have to go in and add a weaker spring. While I'm at it I want to beef it up a bit and have it shoot 330-350fps using .2s and about 15-20RPS on a 7.4V lipo. In my tests using my 7.4V lipos, the RPS is very weak so the motor needs a replacement too. So I am not making a BB hose, just something solid that I can take to CQB games and not worry about anything breaking. So as the reader can see, so far the main replacements will be the spring and motor. Now my two main questions are this. 1. Since I am building a relatively weak build. Do I need to do all the mods such as AOE, cylinder radiusing, mosfet, swiss cheese the piston etc.? 2. Am I going to run into any troubles by simply adding a weaker spring? I remember someone saying that by adding a weaker spring, I may run into problems with the piston and sector gear. Any word on that? I do plan on this being my thread to show how I got my gun from stock to what I want it to be and I hope that everything turns out. Edit 1: I don't want to replace any parts unless I have to.