Having built guns since the 1800's, I get the impression they know all about carbon steel. At one point there were no stainless guns at all. If the 438 in question is the scandium model then it's actually an aluminum alloy with scandium included, not all scandium. Most metals used in guns are alloys, carbon steels are used as they machine readily with less tool wear than the stainless varieties and reduce costs.
Note the exact meaning of "stainless," ie, to discolor or corrode less than something else, typically carbon steel. It doesn't state stain proof, and in contact with humidity, sweat, salts, etc it can discolor and pit. It just stains less. Parts are usually dead soft, not tempered, because extensive firing would heat them up and draw it, leading to critical softening and loss of the intended strength. If they did employ that in some way it would be nice as it would take less mass to contain the cartridge under ignition, but, alas, such is not to be. Ergo, lighter alloys are marketed, which have the distinct drawback of increased recoil.
Nobody minds a light carry weight gun but after a cylinder of some hot +P they consider their ammo choices more carefully.
I've read somewhere the difference in weight scandium to aluminum is about the same as large rubber grips vs slim wooden ones. There are diminishing returns in weight savings with some choices, as noted above. Note that some sources of information over components are as dated as production, over the years S&W changes from one to another and it needs to be pinned down to that specific one.
