That's a mighty interesting design and I can see what the thought process was, to create something that is at the same time a driving band and an aerodynamic nosecone, but I'm assuming it also worked poorly in practice and was quickly abandoned, because I can also see a few ways this could have gone that way - for example if the copper sheath isn't exactly straight on the shell body or if it's too thick on one side, it will absolutely cause it to wobble in the barrel and create all kinds of amusing gyroscopic effects in flight. Also, copper is very expensive compared to steel.
Also, I'm not sure, but the body itself looks very much like a 37mm Bofors, so it might be possible the thinking was to reuse the same casting but to bulk it up to 40mm with that combination driving band/bourrelet/nosecone.
I'm also not sure how they thought to secure the sheath to the body against rotation, because while I see a crimping groove with some vertical crimps in it as well, I'm not sure that's enough.
Finally, the holes - since there are holes in the fuze as well, could that be demilling?