Ultimately, the whole cast vs. forged thing is just not a meaningful discussion. All of the small parts (hammers, sears, lock plates, triggers, safeties, and so on) are that wonder material of the late nineteenth century - low carbon steel. It makes no functional difference whether the steel that will be shaped to make those parts arrives as a casting or a forging; it will be filed into the shape desired and then either surface carbonized (as in the case of the hammers) or flame hardened (the triggers) to the desired hardness.

And that hardening, when not done properly, is whence we get the myth of 'soft steel'. All, and I do mean all, low carbon steel is soft and easy to work. That's why it is the preferred material. The problem is when the shaped and finished parts are not correctly heat treated (or heat treated at all).

To understand how this absence of heat treatment happens requires understanding Spanish artisanal shotgun making. It's not an industrial process, it's an artisanal process. Improper heat treatment isn't particular to any specific maker, to any identifiable period of time, or to any particular model of gun. Improper (or absent) heat treatment happens when an artisanal maker is faced with filling an industrial scale order. Artisanal processes just don't scale up well.