You're confusing metal treatment that hardens the metal with treatment that imparts colors on the surface of the metal.
While the hammer and trigger ARE case hardened (I think to at least some degree, but it's a brave new world with sintered parts), the surfaces are also color case hardened.
In the old days, those wonderful blues, reds, yellows, greens, etc., the case hardened colors, were part and parcel to the case hardening process.
Now days, not so much.
In order to destroy the case hardening, the layer of hard metal surrounding the softer core has to be either heated VERY hot, or it has to be physically removed by filing or grinding.
You're not going to do that with bead blasting.
If anything, bead blasting can make the steel even harder by "working" the metal.
The color patterns on the trigger and hammer, though, those CAN be removed by bead blasting, because they are, essentially, surface oxidazation.
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