re: 9 year old son. Right handed, left eye dominant.

Damn. I didn’t think it was as common as it seems. I’m same way. As a kid with single crack barrel I could hit shooting right handed. Once I got my first full size shotgun at 10 and missing a few ducks on water, I tried left hand and was good to go. I eventually switched to left hand shotgun because of enough powder in my eyes. All my rifle are right handed though.