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