It will be a lot easier to just link this thread when similar questions arise in the future, so I thought I'd add Robert Churchill's How To Shoot written in 1925. "The Master Eye" is Chapter VIII
In the normal man the degree of "master eyedness" is slight. What is not so well-known is that fatigue of the master eye rapidly transfers the mastery (temporarily of course) from one eye to the other.
If you strain and weaken the command of your right eye by putting your head down to the stock of a badly fitting gun or by a bad habit of gunmounting you tire the eye.
After a few such shots the right eye is fatigued and the left then takes mastery.
(His interpretation of transient dominance switching)
In practice at other sports this eye problem does not appear to cause trouble. Left eyed cricketers and tennis and golf men all probably exist but only in shooting do we hear of it as a dreadful physical problem.
(Interestingly, today we believe cross-dominance may be of an advantage in baseball, cricket and golf.)

If you learn to shoot without contortions and strain you will be in the same position as the ordinary man who uses his eyes all day without any perceptible strain or discomfort. By adopting a natural head position 75% of the master eye difficulty is solved.
If, on the other hand, you are completely left-eyed...(a "left-eyed" gunstock) will compensate for the trouble...

https://www.trapshooters.com/threads/robert-churchill-eyesight-and-the-master-eye.910472/