Well, for a pure hunting gun, I cheat. I overlay ivory on the front sight for good visibility. And for a rear sight, regardless of authenticity, I take a full buck horn, heat it and bring the tips nearly to touching. I then use a mandrel to make the hole perfectly round. Sometimes I will shorten the tips, to be able to make a smaller aperture.I don't cut a notch.
I use the full rear sight as an aperture. Being still an open sight, it could still theoretically be used for competition, but that isn't my purpose.
There are also silhouette rear sights that are made that are tall and square profile, with a thin slit in the center. These are also good for this purpose, as it allows you more leeway in making the aperture smaller if it suits you.
I'm getting older, and having a harder time seeing notch sights. The method I use is very fast for getting on target, gives a good sight picture, and finally and most important to me in a hunting rifle, it works!