After reading this thread and others I went to the range today and tried some range grade Federal 40 S&W in my 20SF. Functioned every time although the brass only ejected a few feet. Reminded me of shooting 38 wadcutters in a 357 Mag - very little recoil compared to a hot 10mm load. Only having a 50 yard target available today the accuracy was not as good as the 10 loads but I'll try again at shorter range next time out.
With Wal-Mart selling 40 S&W for around $27 per 100 my 20SF will be getting a lot more range time.