Actually, the hammer is not even nearly "half-cocked" when at rest on the hammer-block safety.
There is hardly any tension on the spring at all compared to when it is brought to full cock by the trigger linkage, and again by the slide every time it is fired.
Look in the open slot at the rear of the slide and you can see the hammer at rest on the hammer block.
Now, making doubly sure the gun is un-loaded, slowly pull the trigger.
You can see the hammer being brought back to full-cock and released. Without that full range of hammer movement, there is not enough energy available to fire a round, even if the hammer-block safety did somehow fail. (although it is very hard to imagine it failing)
Now that the hammer has been released, it now rests inside the slide, against the firing pin recess in the slide.
Slowly open the slide, and you can see it press the hammer back all they way to where it would be at full-cock if it could stay there. (But it can't, because there is no internal sear to hold it there.)
Now slowly ease the slide forward and you can see the hammer follow the slide until it is once again un-cocked and resting against the hammer-block safety.
Only by pulling the trigger is it possible for the hammer to come to full cock and be released with enough energy to fire a round in the chamber.
(Or put any stress the spring at all!)
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