The hole pattern seen in the lower sketch is for the vernier plate.  When the 22 1/2 degree hole pattern in the washer on the upper right is rotating on top of  the vernier plate, there will always be a locking combination available every 7 1/2 degrees.  The plate with all those overlapping holes is clearly no way to achieve our 7 1/2 degrees.   The direct approach will not work.   Locating them at the required interval for strength in the washer needs something like that six hole layout seen in the vernier plate.  (Click to enlarge.)


And as always, our experiments have shown the need for at least 7 1/2 degrees of incremental adjustment to tune the machine properly.  (I keep repeating that I know, but it really is very important if you want an accurate shooting machine.)

Note how nicely those sixteen locking holes nestle in the rim of the washer, relative to the four holes occupying the interior of the artifact’s end cap — different hole patterns with different purposes.

The four holes near the spring hole are 7 mm in diameter, sized and located per the artifact. The smaller of the two concentric circles in the center represents the spring hole.  The slightly larger one is in the vernier plate.  The difference between them is the rebated portion that the washer flange rides in.  Interesting that the room provided by the artifact not only allows this arrangement of the two circles , but also seems in terms of material distribution to be of just about the right sturdiness. All is to scale.

If you ponder this geometry for a bit, and try and think of equally plausible options that answer to all the facts, the logic of this layout is undeniable.  Really there are no better alternatives than supposing the existence of a vernier plate.  QED, or some such.