A few points to add. First Steve Fuller had access to a good deal of ammunition and components from Gordon Ingram’s estate My guess would be that he put these in the auction.
I did receive a sabot 9mm bullet with a steel core and unheadstamped case that reportedly came from the Ingram estate.
In 1973, I visited Jeff Werbell, the son of the owner of MAC/Sionics. That evening he opened a ammo storage room in their home and showed me some of the interesting stuff. That was the first time I had seen the 6 round tin of the HE 45ACP rounds made for the US government. He had lots of very interesting stuff. One that I remember was a wooden block with holes drilled in it which contained 9mm cases with bullets in them. The block would hold about 20 rounds and there were about 10 in it as I recall. What struck me is that all had a single number headstamp, though I can’t remember if some had more than one number. I remember that there were no two alike. Jeff told me they were development items and a set for some purpose. I don’t recall what. I thought they were brass cases, but the light wasn’t great. The photos by Joe and Zac remind me of these rounds. I wonder if they were actually steel cases.
I tried to talk him out of one or all of these with no luck that evening, though I did leave with some interesting items. These were something special that he couldn’t let me have. Not long after I went to the UK for a tour and lost track of Jeff. About 8 years ago, I looked him up again, but he is long out of the ammo business, though he did have a few ammo cans of old leftover MAC ammo that I looked through. The rounds above were not part of that, and Jeff could not remember them when I asked about them. Apparently they were long gone. Maybe they have no relation to the items Joe and Zac are talking about.