I replaced the stock rebound spring with the one from a Miculek kit, and it resulted in a surprisingly noticeable improvement in perceived trigger pull. During my experimenting, I went back to the stock ribbed mainspring in this 627PC, because installing the Miculek main spring along with the reduced power rebound spring resulted in a sluggish trigger reset.

So, now I'm very happy with the combination of the stock PC ribbed mainspring and the Miculek rebound spring... I'm wondering - is there any downside to this lighter rebound spring? The trigger resets just fine, even when the gun has been shot a lot and is getting dirty, so I can't think of any reason this would turn out bad for me in terms of reliability.

By the way, does anyone know the spring weights in Miculek's kits made by "Bang"?