I own a S&W 625 Performance Center with a pull trigger of 3,5 pounds. Possible to reduce at 2,5 just changing springs or need an expert gunsmith to do that?
I have 3 625s that are used for competition.
All have lightened triggers.
Springs are only part of the job. Some judicious polishing is usually needed.
It's not too difficult to do, but avoid areas that must not be touched. Jerry Miculek's DVD on this subject will guide you.
Be advised that you may need to use only Federal primers if you do tune it to very light (fast).
Any pistol that would be used in any kind of competition where you draw from a holster should have at least a 3 1/2 lb trigger pull. Any lighter and you are asking for a "ND". A bullseye gun, due to how they are handled may be lighter (NRA rules limit weight). Think safety first.
It's hard to answer your question accurately without knowing how much this particular Revolver has been fired and what the PC has actually done to it. If it is one that is new out of the box then it WILL wear in and smooth out with shooting after a while. If that is the case then spring changes will only help so much and burrs and rough spots must be addressed as well.
If this is a revolver that has had thousands of rounds through it then the springs might make a bigger difference then if the Revolver is new since many of the wear parts have already been sort of smoothed out to an extent.
I do not own any PC guns and so I am not really familiar with exactly what the PC does to actually make it a "PC" gun. You might want to actually call them and ask.