I just measured 7 new green recoil springs (which are all I have left at the moment for new springs I keep on hand for my own CS45). They measured from 3 7/8" - 4".
A small amount of shortening (spring set) is expected and normal after the recoil spring has been installed in the gun.
I typically replace my recoil springs whenever they get to be at least 4 or more "coils" shorter than a new one ... or every couple of years ... or somewhere between 500-1000+ rounds. Just depends. (Sooner than later if I've been using +P loads in the little CS45, but now I save those for my larger .45's.)
That's just me, though. None of the shorter recoil springs I've replaced had been causing feeding or functioning issues, although feeding was "brisker" upon installing the new springs. I simply prefer to replace recoil & mag springs in the 3rd gen guns
before they start to exhibit signs of having weakened to the point where they no longer provide for normal functioning. That single, short flat coil spring is asked to do a lot in the hard recoiling little CS series guns.
Nothing had changed in my last armorer recert regarding spring replacement. The normal recommendation is to replace the CS (and all 3rd gen) recoil springs either every 5 years or every 5000 rounds, whichever occurs first, and which seems a reasonably prudent and conservative recommendation. I tend to lean toward an even more conservative periodic replacement, though.
The springs are very reasonably priced, so I order a dozen or so at a time. (But then I probably shoot mine more than the average owner.)
Granted, I buy mine at a small discount as an armorer, but even paying the retail of $3.26 seems like a small cost to bear when measured against the cost of the ammo used during the service life of any recoil spring.
My mag springs seem to last a little longer before they get significantly shorter, meaning a bit closer to the
normal recommendation for a replacement interval.
