I attended the S&W pistol armorers course in about 1991. Just from memory, without checking my notes:

The instructor told us that the FBI had required that the point of the trigger that contacts the draw bar be longer in order to reduce take-up. The trigger was the only part different from normal production.

The pistols "locked up" when that longer trigger would over-ride the draw bar - holding the draw bar forward, which in turn held the hammer down so that pistol could not fire and the slide could not be retracted.

While the special trigger was specified for FBI pistols, some went out with regular production pistols, too.


"Trigger Staging" in this notice.