I had in my selection of castings and my spares box, a choice of two whitemetal dome castings. While I had a third options of turin a up completely new dome from brass or nickel I decided to see if I could clean up the fairly mediocre castings. I was able to grip the locating pin of the first one in a collet and it didn’t actually take much material removal to clean up the first casting (I measured it at 0.3mm overall)

Buoyed up with the results of the first one, I had a go at the second casting which was much better and only required a clean up of the top to remove minor pitting.

Now I have a choice of two to fit.