The take-down pin falling out seems to be a common problem these days and I've seen lots of posts on various gun forums by disgruntled BG owners. Some people have had to send theirs back to the factory twice for the same problem. It appears that S&W doesn't have a clue as to what is going on or how to fix it. Stay tuned....

Edit: What kind of ammo were you shooting when you had the misfires? Did the ammo fire after several strikes?