Picked up a G20 gen 4, and a stainless steel guide rod in stock weight (17lbs I think?) Gonna be one of my woods carry sidearms. So I also acquired a 6" Double diamond stainless steel barrel from glockstore and a 20 pound RSA from brass stacker, all to accommodate Hard-cast projectiles moving at high velocities. My question is, at what point do I need the 20 pound spring as opposed to the factory weight? It is a combination of bullet weight and velocity no? Please and thank you very much in advance.