I’ve been requested to provide additional photos of the powder measure setup. As with the other page, clicking on a photo takes you to a larger image.

This is an overview of the setup, sorry about the focus. As you can see, the disc measure sits at the proper location and orientation for the arm to go into the flat hole.
Here is a closer look
Here are the pieces of the powder measure arrayed neatly. The next image labels them.
Here I’ve taken the tubes out of the parts of the die and powder delivery system.
The only place there is any play in this system is where the tube from the riser fits into the tube for the expander. When the expander is in the die, the riser body keeps the tube in the riser from completely meeting the expander tube (about ¼ inch play). This seems to be about the only play in the system and I think if it weren’t there, the problem might not exist.