In the case of the ".45" the OP may be speaking about the model 1911 and
the changes Colt adopted when going from the series "series 70" and older
pistols to the "series 80." The "series 80" guns have a plunger & linkage
that blocks the firing pin from moving forward if the trigger is not
depressed, and also changed the half-cock configuration somewhat. Some
other manufacturers of model 1911s have adopted these or similar
changes too. With the older designs, it is possible that with a round
chambered, if the pistol dropped onto a hard surface at the right (wrong?)
angle with enough force, it could fire. Note that these accidental discharges
are not from the "hammer ready to fall" but from inertia moving the firing pin
with enough force to strike and fire the cartridge primer. (The hammer might
fall in some cases too, but that would indicate something in the gun was
broken or modified incorrectly)



--
There are no stupid questions, but there are lots of stupid answers.

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org