kbm6893-the metal frame S&Ws operate the magazine disconnector with the top of the magazine lips. Whether or not your particular pistol requires the mag to be locked into place depends upon magazine spring tension and individual tolerances. We issued the 1006 and it didn't need the mag locked into place to operate (did bang, whoops a couple of times myself).

The M&P series uses the back of the magazine body to operate the disconnector, so the magazine position isn't as critical.

Buff- I read a similar story once upon a time (but IIRC, was one officer, not 2), I don't believe that Mas was the source, since he's debunked several similar tales involving either the thumb or magazine safety. More to the point, he participated in a discussion similar to this on what's now the eotacforum back in October 2006 where this issue was beaten beyond death without mentioning it. He's currently traveling/teaching with only sporadic internet access. One of the other things I remember about that alleged incident is that the holsters in use weren't designed for the S&W, but were used by that department and were alleged to have caused the issue. In any event, without documentation, it's kinda like the story from your cousins uncles brother who knew a guy...............