S&W revolvers have had an internal hammer block for the last 90 or so years, It is a block of steel, connected to the trigger, which bears against the frame and forces the hammer back when the trigger is not being pulled. The only way you get one of these guns to fire is to strike the hammer hard enough to break it in half. We're talking about a piece of hardened steel 3/16" thick and 1" wide. :eek:
There is also another piece of steel, connected to the trigger mechanism, which is between the hammer and the rear of the frame when the trigger is forward.
These guns have always been perfectly safe to carry fully loaded.
Modern S&W revolvers must pass a drop test to be sold in many states, such as California and Massachusetts.