As title, BEEMAN/WILLIAMS peep sight. Dovetail fitting and fully adjustable, it looks like it will fit the smallest to the largest dovetails.
It's the micrometer adjustable/target turrets model, which I don't believe is available new anymore.
It's in very, very nice condition, and certainly wouldn't look out of place on a mint rifle.
Images here, here, here, here, and here.
Last edited by master_shriller; 30-03-2018 at 04:44 PM.
master(dot)shriller(at)gmail.com