CajunBass, it has to do with the nature of the mechanisms. Firearms have to be positively cocked in order to fire at all; it takes a certain amount of effort to get the gun into firing condition. It's not something that can happen by gravity, or by jiggling the gun around, or by something breaking inside the gun. Some positive effort has to get the gun into firing condition. The springs have to be mechanically compressed, or the hammer has to be pulled back.
In the case of a firearm which has already been cocked & then locked, the lock might fail, but the gun still requires pressure on the trigger in order to fire because modern firearms have firing pin blocks which prevent the gun from firing if the trigger is not first compressed. There is simply no mechanical way for any gun to fire without the gun first being cocked, and if the gun is cocked, it still won't go off without at least two other parts breaking, the lock and the firing pin block.
Incidentally, the firing pin block on most models cannot really break by moving out of the way. On most guns, the firing pin block must be mechanically moved out of the way before the gun can fire. So if the firing pin block breaks, it's going to break by being locked into place (preventing the gun from firing at all), because the block is always in place unless some mechanical action moves it.
An integral lock, on the other hand, is only one part. It's the only thing that has to fail in order to prevent the gun from working. And it can fail without really "breaking," simply by jiggling into place. Every company has a slightly different design for these locks, but -- for example, and to keep on topic for this thread -- the Taurus lock is a C-shaped piece that catches an opening along the slide rails when the C is swiveled around. In place, it keeps the slide from moving. It doesn't take much imagination to picture that getting jiggled into place and locking the slide accidentally, if the mechanism has loosened up in some way.
pax
In the case of a firearm which has already been cocked & then locked, the lock might fail, but the gun still requires pressure on the trigger in order to fire because modern firearms have firing pin blocks which prevent the gun from firing if the trigger is not first compressed. There is simply no mechanical way for any gun to fire without the gun first being cocked, and if the gun is cocked, it still won't go off without at least two other parts breaking, the lock and the firing pin block.
Incidentally, the firing pin block on most models cannot really break by moving out of the way. On most guns, the firing pin block must be mechanically moved out of the way before the gun can fire. So if the firing pin block breaks, it's going to break by being locked into place (preventing the gun from firing at all), because the block is always in place unless some mechanical action moves it.
An integral lock, on the other hand, is only one part. It's the only thing that has to fail in order to prevent the gun from working. And it can fail without really "breaking," simply by jiggling into place. Every company has a slightly different design for these locks, but -- for example, and to keep on topic for this thread -- the Taurus lock is a C-shaped piece that catches an opening along the slide rails when the C is swiveled around. In place, it keeps the slide from moving. It doesn't take much imagination to picture that getting jiggled into place and locking the slide accidentally, if the mechanism has loosened up in some way.
pax