R S,
I respect your input. I have been proven wrong many times, and I have always made it a point to never treat an opinion as a fact. I agree when you state the frame/slide would have cracked regardless of what recoil spring was being used. You don't have to look long to see cracked frames in virtually any auto loader, Glock, S&W, Colt, Springfield, CZ, etc. Quality control is only as good as the person(s) overseeing the process and metallugy, proper hardening/surface treatment, and machining (sharp edges can produce stress risers), reloaded ammunition, all enter the equation. Sometimes things just happen.
If memory serves me, it seems most of the Witness problems are with the 10mm, which is a very high pressure round. I need to look up the SAAMI operating pressures for the 10mm. The 10mm is offered on the same platform as the 9mm. I have a feeling Tanfoglio should have built the 10mm on a more robust frame/slide. Browning increased the slide thickness and beefed up many components to go from 9mm to .40 in the Hi-power, and the .40 is basically a "10mm lite".
As far as the heavier recoil spring reducing felt recoil, I gleaned this from "1911 Tuner", a well respected gunsmith that posts on the High Road Forum regularly. I'll see if I can dig up some of his posts on this matter. He provides a really good detailed step-by-step analogy of the forces a to heavy recoil spring imparts on felt recoil. Not saying your right or wrong, I just need to back up my alligator mouth to cover my hummingbird b_tt.
Your points are valid and I'm glad you mentioned dropping a slide on an empty mag; a big no-no. Your comments are excellent.