Wilson Combat 22# flat wire spring (10SEN22)
I added one of Wilson Combat's Sentinel flat wire recoil springs (10SEN22), that BMCM mentioned previously, to a recent order from them to see what they are like.
It is almost exactly 4.0" long out of the box & has (21) turns. The one end is closed (double coiled) but the opposite end is not & undoubtedly was cut-down from a longer spring.
Not having a CS40 or CS45, the next closest pistol I have is a 4013 (non-TSW) to try it in. It has a 3-1/2" bbl vs the 3-1/4" CS45's and both are a large frame compact.
Using the same test setup as I've used before I tried the W-C 10SEN22 (22#) recoil spring in the 4013 to compare it to my other prior recoil spring results.
Installed in the 4013 no stacking was found, the slide's rearward action stopped on the frame abutment, not the compressed spring.
It did not register as strong as the Sprinco dual/nested spring set I tested previously (which registered almost identically to a factory S&W dual/nested spring set; these springs are also used in the 4516 as well as the 4013).
And compared to an ISMI flat wire GLC-22 (22# strength & 31 coils) it was slightly less powerful.
After testing, the W-C 10SEN22 had a set spring length of 3.6"
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For the heck of it, I also tried it in my CS9 which is a medium frame & has a 3" bbl.
It measured several pounds stronger than the factory 16.5 turn flat wire spring but there was moderate stacking on this shorter guide rod; the slide was stopping on the compressed recoil spring, not the frame abutment.
No idea how many coil(s) would have to be cut-off to fix that but doing so would surely reduce it's strength accordingly.
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For clarification, the (A) and (C) condition readings in my tests below are fully a by-product of the recoil spring only; early partial force & full compressed force.
The (B) condition reading is early partial recoil spring force with the majority coming from the mainspring's force on the hammer against the slide.
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In the 3-1/4" bbl. CS45 slide the W-C 10SEN22 would likely be a little stronger than in the 3-1/2" 4013 (since the space is shorter) as long as there was no stacking, requiring the spring to be shortened.
Seeing that the CS40/CS45 use the same flat recoil spring (263310000) and that the their slide/barrel assemblies are shorter/lighter than the 4013 I tested in, I would think that the factory CS40/45 recoil springs would have to be stronger than the factory 4013 springs to do the same job?
If so then it would appear the the 10SEN22 spring may only pick up a few pounds of force in the CS45, essentially only matching that of the factory 4013 springs.
Not having a CS45 spring to compare to I have to wonder if the 10SEN22 would even match it's strength?
I'm sure BMCM can add more when he gets a CS45 spring in his hands to play with.
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Of course, he said that they'd also bumped up the rating on their P90 recoil springs by that time, and were no longer using the same spring they also used in the P89 (9mm).
Then, after finally getting the right springs shipped following the wrong ones shipped, they didn't get the quantity right. I had to call again and get them to ship more springs, like were listed on the original order (when they shipped the wrong springs). 
