As far as I can tell, the spring guide stopper isn't hardened, the piston sear and trigger however are. This makes sense considering that the spring guide stopper and spring guide are more or less fixed parts and therefore don't need extra hardness.
Seeing that Blind Sniper already did it, I think you can do it as well.
Seeing that Blind Sniper already did it, I think you can do it as well.
