I think I've got it. You will notice that the 4006 is one heavy dude. Now, cock the hammer, and imagine dropping it (hammer first) on cement. If any part of the hammer is going to break, the "tip" will break off (the hole makes the thinnest cross sectional areas) leaving a functional hammer (like a bobbed hammer).
The older, bar-stock style hammer has the thinnest cross-sectional area down near the pivot, and if dropped hammer-first everything above that would break off. That would leave the lockwork "functional" but nothing to hit the firing pin.
The newer style MIM hammer looks like the tip should break off too. Like a Sig P6 hammer, except the MIM S&W hammer has a closed web in the middle.
The older, bar-stock style hammer has the thinnest cross-sectional area down near the pivot, and if dropped hammer-first everything above that would break off. That would leave the lockwork "functional" but nothing to hit the firing pin.
The newer style MIM hammer looks like the tip should break off too. Like a Sig P6 hammer, except the MIM S&W hammer has a closed web in the middle.
