I have edited this from the original post to replace the sketch with pictures and make the text match them.
I picked up this shell (on right) at SLICS, in a bulk buy. It’s shown next to an AA with standard height low base for comparison.
The cup is only 3/16 high and is strongly reactive to a magnet but appears to be washed with aluminum. The hull is the one piece compression-formed plastic, typical of other shells I have dated to the late 1960’s. I know Olin experimented with aluminum a lot, I have some paper hulls with aluminum cups, but this is a washed steel and I’ve never seen any from this period (aluminum washed). I’m thinking this is an experimental or limited run. Comments welcome.