I think that sight is for a Mannlicher-Schoenauer rifle ("MS"); those rifles were imported and sold here in the 1950's and 1960's but are no longer in production. They were expensive and never common. If I am wrong, I have no idea what else it would fit.

Jim

 

Wow, well that would make it a really usefull sight, now wouldn't it! I have no idea where I got it, at a gun show I suppose. What the heck possesed me to buy that? I hope I didn't pay much.
Want to buy it?
Actually it's a nice peep sight for the left side of something, it has a longesh bar coming out towards the front with two holes for mounting. The mounting bar/base area has a radius to fit a curved receiver.
I bet somebody is just itching to buy it!
Jim S.

 

The Lyman 57MS is for various Mossberg 22 rimfire rifles, it was introduced in 1938.

 

The one I have is somewhat similar to that picture, but definitely not the same. Mine seems to be a newer design, the bar that sticks out to the front is not as wide and has two holes. The horizontal and verticle adjustments are considerably different on mine also. Maybe they used the MS designation for another purpose later on, like the Man. Sch., or they just re-designed it. Mine has the aluminum indicator plates like newer ones.
I wish I could put pictures on here, but my Brownie Starflash camera just won't cut it.

 

GunHugger is on the money.

According to the Lyman sight selection chart (Shooters Bible #60, p.385) the 57MS is for Mossberg .22's.

 

Here's a better picture.

 

Yup, that's it. Looks like it was moved back on that rifle.

 

Do you still have this sight? for sale?
Pm Sent

 

It was sold to a real good guy on this site a while back - thanks.