I got mine from MVA and they are set up like an original Winchester so you tap both screws which is actually better. This way if I take the sight off I can put filler screws in it and it will be like an original and not have a screw drilled into the tang lettering. If I sell a gun I don't intend on 500-600 dollar worth of sights going with it so if they are tapped like the originals the sight bases will interchange between Uberti or original Winchester's if I should want to switch the sights to another gun.
Cliff I guess I'm not following. You tap both screws (back and front of tang sight ) that goes into the receiver tang? And I didn't even think of the fact the front tang sight screw will go into the lettering of the "model 1873" stamp. I just was kind of confused. Sorry. And what and where is MVA?
Just a note of clarification. Not all original 1873s are drilled and tapped for a tang sight. I don't know for sure, but it may just be rifles, not carbines. My original 73 carbine made in 1892 is not drilled and tapped for one.