Those are factory swing-off mounts. I have made several sets of those mounts for customers for different size scopes. When made properly, they swing smoothly and return to zero perfectly. I make the front ring first and then mount the scope to the rifle with the front ring only. I then measure the gap between the top surface of the mount and the bottom of the scope using slip gauges. Using this dimension the rear ring is made to exactly the right height. This way they swing and return to zero perfectly.

Waidmannsheil