I have seen references to this bullet being lathe-turned from 90/100 brass rod. However, in examining loose bullets the only sign that I can see of lathe turning is in the area of the crimp cannelure. The remainder of the surface, ogive, boattail and base looks more like it was swaged from a solid slug.
There is a short film, linked from this website but I cannot find it at the moment, which shows the machining of these bullets but only shows cutting of the cannelure. The part-formed bullets have a distinct web or skirt around the centre, perhaps excess metal displaced when two swaging dies, one for the ogive and the other for the boattail and base squeeze the slug into shape. The collar is exactly on a level with the cannelure and is neatly removed when the cannelure is cut.
Does anyone have information on the manufacture of these bullets? I do know that the UK contractors had great difficulty in producing this bullet.