This is a pretty strange "tang sight". It's made to mount on the tang area of a Ballard rifle, and accepts a modified Lyman receiver sight.





The receiver sight is milled with two receiver slots, and a large thumb knob to secure the sight. The back of the mount is milled with two rails that have positive stops to return the sight to zero when removed and reinstalled.



Craftsmanship is very nice, and the base appears to be a nicely finished casting that is blued. Spacing is the standard Ballard 1.125" holes. The Lyman has 125 minutes of elevation, which should be good for most mid range work.
Wonder who made them, and how many might have been made?

here is some speculation on my part, I think that the base may be from a Lyman 48 for a Winchester Model 52, maybe the slide as well. The part that attaches to the tang could be a casting with machining done afterward or it could involve no casting and just a fair bit of machining and hand fitting and filing.

I would say that whoever made it had access to at least a milling machine and most likely a lathe as well (for the knurled screw).

The base that attaches to the rifle shows signs of casting on front and rear edges, so it did start life as a casting. The rest is nicely machined, and to such a close fit that even when the securing knob is loosened, the sight and the base have no play between them.
Did the Win. 52 use vertical mounting screws? Thought they were horizontal? And since the back of this sight is flat, and appears to have not been thinned, I'd guess the sight was for a flat sided receiver like a Martini, or one of the old lever guns from Marlin, Winchester, etc.

Most Lyman 48's have horizontal holes for mounting. One underneath the slide, the other on the side of the slide.
However, on some for the Model 52 target, the sight mounts
on the rifle using a large dovetail. Here is a link
to a picture of that kind of Lyman 48

Lyman 48 for Winchester 52 target

You can see that there is no hole by the side of the slide.I can imagine removing the rail with the dovetail. I don't know what the back of this particular model looks like.

Thanks for the picture link. It appears the Win. 52 Lyman sight has the bottom edge of the sight beveled at a pretty good angle to clear some part of a 52? So guessing this sight isn't quite the same model.

That sight is pretty cool.