They could be, I've been doing some study, the old trapdoor Springfields had bronze firing pins, I believe I found a reference to aluminum bronze for firing pins from 1912, They were cast, then hot forged. Many things I thought were kinda new have been around quite a while. Brass would most likely be too soft, though I'm finding out how ignorant I am in this study.
I have CNC produced 416 stainless triggers to replace the plastic triggers on Colt Mustangs, Mustang Plus II's, MK IV Government .380's and Sig P-238's. Video on installation in Sig;http://www.youtube.com/watch?v=Jh2v_-87DRM
Also I made up a hundred Llama .32 and .380 recoil spring buttons, checkered nicely and blued.