Eye dominance
I know that this is going to get some comments, but have him try shooting with BOTH eyes open. Shotgunners do it all the time.
With a bit of practice, it is quite possible and easy to use a scope with the non-dominant eye.
Since he is right handed, the shooting left handed tends to feel "wrong" and awkward, so a left handed gun is not really the way to go.
One of the best target shots I knew used offset iron sights, mounted to the left side of the action and barrel, (In case anyone wants to laugh, have they shot a Bren Gun?) so accuracy can be obtained.
Actually, when you think about it, how many of us have shot using the "wrong" eye while hunting, and you had to shoot "wrong hand" when you position didn't allow you to engage your target due to an obstruction or the way you were facing.
It's something that can be overcome.
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