Daan - thank you How dumb of me. After 36 years working in a good gun shop, where we had at least several SCI members, you would think I could have figured that out. Ahhhh, senility - I DO love it so!
My sole defense is despite being a shooter since ten years old, and a cartridge and gun collector since age 22, I have never been a hunter. Nothing at all against it, just not my cup of tea. I got away from gun collecting in the 1990s, pretty much, but never gave up cartridge collecting, although I have, from time to time, pared down my collection.
I suspect that many collectors don’t know about the SCI cartridges, as I think the rounds made went with the rifles for them. They might have been hard to get if you didn’t happen to know the fellow who ended up with the rifle. I could be wrong about that, but I have never seen any of them, to my knowledge, and I have looked at a lot of cartridges in my life.