Shot 3 different unreliable Beretta M9s, but never saw one actually break anything. That was in the Army years ago, and in fairness for all I know the armorers replaced the mag springs with off-brand spaghetti or something.
(The 4th one was an awesome gun.)
I had a Glock 20C break a slide stop. What? A Glock break?!?!
(Other 3 Glocks never broke anything.)
Had a S&W 610 Classic break the firing pin right off the hammer. Who said revolvers don't break?!
(Once that was fixed it worked, well, like a good 'Smith revolver.)
Had a Colt eat an extractor once, entire front end of the hook came of... this being a mid-1990s Delta Elite. Replaced it with an AFTEC and tried real hard to break it again, but failed.
(Other 2 Colts were shot to hell and never broke anything.)
Technically, my old Para-Ordnance P14-45 didn't break anything, but only because it never worked, and so never had the chance to. Had a Kel-Tec P32 break before I could even shoot it... hard to beat that.
Bottom line is, it seems like almost anything can work, or not work. You've really got to take guns one at a time.
EDITED TO ADD: Actually, I broke a chunk off a Glock sight, too.