Daryl,
it is extremely tough to take pictures of the muzzle that are sharp in depth and show as much details as possible. I had to use very limited light to be able to make anything of the muzzle threading visible, therefore it also looks as if the muzzle part is dark and pitted - which it isn't. It looks as if the cuts were made into the choke at the muzzle, and as you had noticed they are shallow and in fact deeper at the top and nearly invisible at the bottom. I had originally thought I had mentioned this in my starting post, but obviously I forgot - sorry. But to get back, basically you can't measure any real difference in the cuts nor outside of them. It is also very tough to tell how long the cuts are exactly since there is no real starting point.

4seventy,
it therefore looks as if the dimensions you had named would be quite close to the dimensions I had measured. But would the bullet have a smaller diameter than the rifle muzzle diameter?

I have hardly ever seen such a beautifully made rifle. The color case hardening is exceptional, as well as a simple but nevertheless beautiful engraving. The extreme light weight is another big plus of this rifle. There had not been a single day since purchase where I have not taken it into my hand. It is just satisfying to handle and look at it.