Will a complete 9mm slide [ slide barrel recoil spring ] work on a .40 frame. Are the ejector and extractor different?

All you really need is a factory 9mm barrel. At one time, I owned both a 9mm SP2022 and a .40 SP2340. I tried the conversion and it worked well enough that I sold the SP2022.

Thanks Gary.

Frame is the same, slide internals are a bit different. You'll also need a 9mm mag.

People have reported it'll chamber and fire just fine, but with the extractor not sized/positioned properly for a 9mm cartridge, you may have extraction failures. Probably fine for plinking, but I wouldn't bet my life on it. I'm looking for a 9mm slide for that very reason.