To get the barely over 5 lb DA and soft and crisp SA break you need to do more than just replace the springs. There's a couple of web sights out there with complete guides to how to stone the rubbing surfaces and tune up the action. They are a google away if you search for "cz trigger job". But such work is not something to do if you're not up to the skills and understanding how important the angles and shelf dimensions are and how little it takes to ruin the works. It's certainly not a Dremel and polishing wheel extravaganza.
The mainspring going to 13 lbs is the big one. Also the trigger return spring is wound up more than it needs to be. WITH CARE you can field strip the gun, reach down and lift up and back on the return spring to deform it just a little and take off some of the return spring tension. Do this with care and take notes on how far you lift and bring it back and next time go about 2 mm more then release and try the trigger. Work it around in small increments like this until the return pressure at the trigger is about half what it was
If you go too far with this the trigger won't reliably reset back. In that case the trigger hinge pin needs to be knocked out to let all the trigger guts come out and you'll have to form the return spring back the other way a bit.
While you won't achieve as smooth and clean a trigger as with the full meal deal I'd say a good 50% of the results come from the main spring swap and easing the return spring a little.
50% doesn't sound like much you say? You'd have to actually shoot a fully tuned Shadow like I have to see and feel the HUGE difference that a full tune provides. It's almost scary. Most would feel the 50% difference from the springs only and be more than happy with the results.
