I tried it by punching two holes, one smaller than the other, into a sheet of black cardboard.
I tried it on small print that I could not read without my glasses at 8 inches from my eye and it is amazing!
Looking forward to trying it at the range with iron sights on a pre-64 Model 70.
The good news is that with this trick I might be able to shoot a Model 1894.
The bad news is that I don't own one.