I just did some quick trig to get an idea of what the impact of a single set screw screw could be.
If side a is 0.001" (this is the clearance between the breech socket and the tenon
And side b is 1.25" (the length of the breech socket
And it's held together by a single grub screw which provides a pivot
Then the side a magnified to 100 yards becomes 2.88 inches
However in reality they are much looser than 0.001. In fact I have 0.006" of shims stuffed in one
That 0.006 becomes 17.25" at 100 yds
Holy cow