I have had the round in the picture for some time (shown next to a 50 cal for reference). It was recovered by one of my colleagues about 15 years ago from a garden in North London. It was very corroded and I used BIOX to remove the worst of the rust.
I have never known wether it was a genuine solid steel dummy or something someone had turned up on a lathe. With the thick rim it certainly looks like a Madsen type case. The round OAL is 125mm, the base is 23mm and bullet at the neck is 16mm but, because of the rust these are only approximate measurements. I would welcome any views from the forum as to wether it is original or not.
I hope someone manages to turn up a drawing it would be great if the dimensions roughly match.