Interesting Rear Sight

[Winter Hawk]

Anyone know what this hole is for?  This is from an ad for a rifle on another site.  The fellow had another rifle with the same type of rear sight but didn't know anything about it.
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[Ohio Joe]

I don't recall seeing anything like that, but I do wonder if it's a type of target sight, like something that might be found on a Chunk Gun for channeling the front sight through for a better sight picture on one's "spotter" target?

[LongWalker]

Yep.  The idea is that the double notches (one on either side of the hole) eliminates reflection and light scatter, so all you see is a sharp-edged notch.  More of a chunk gun or squirrel rifle sight, but you see them once in a while on other rifles.

[Winter Hawk]

Thank you!  Learn something new every day over here!

~Kees~

[Jim in Wisconsin]

Are the two notches different widths? It looks like they are (I think). Which way is front?

[KDubs]

Hmmm it does look like a larger notch fore and smaller aft.
 Maybe acts like an aperture  of a camera and focus the target.
 ??
Kevin

[Winter Hawk]

LongWalker's answer seems very logical to me.  As I said in my original post, it was in an advertisement for a rifle on another forum.  There were actually two rifles with this sight posted by that seller, which piqued my interest.

~Kees~

[LongWalker]

Hmmm it does look like a larger notch fore and smaller aft.
 Maybe acts like an aperture  of a camera and focus the target.
 ??
Kevin

Camera diaphragm isn't a bad analogy, except it helps focus the rear notch.  You cut the front notch to give you a sharp-edged sight.  Actual measurement of the front notch will depend on the shooter and the thickness of the rear sight blade/size of the hole drilled.