OK......a few of those I've heard/read about, but haven't pursued in any depth.
Steel has never impressed me, and I haven't run it much. My chief concern is effect on fixed chokes or the tubes that replaced them. I've run 12 gauge with Mod and I/C and haven't seen any damage, but my small-gauge guns all have fixed chokes (full) so steel doesn't sound like a good idea.
I am not super-concerned about cost as much as I am about adaptability to small-gauge fixed full chokes--availability of load data and components to support the substituted shot--and getting as close to chilled lead shot performance as possible to enhance that adapability. Once THAT is figured out, I'll see if CA accepts it as legal to hunt with. If the substitute performs closely to that of lead shot in appropriate-for-venue chokes, I'll make practice loads with lead shot like always and use the pricier shot for hunting--much like I load duplicators of my carry loads in sidearms and rifles. If that makes sense.
I GREATLY appreciate this info, sir. It's time for me to do a bit of R&D, and see what bubbles up. If you have some shortcuts or recommendations, I'm all ears. THANK YOU!