buckhorn 
noun [mass noun]
The horn of a deer, used to make knife handles, small containers, and rifle sights: a large knife hilted with buckhorn...
- Sights are a bead front and a buckhorn rear, which I quickly replaced with a Williams receiver peep sight.
- The buckhorn rear sight blocked over half the ghost ring's field of view, which kind of defeats the purpose of a ghost ring.
- The Winchester Model 1892 was equipped with standard buckhorn sights, while the Marlin had been fitted with a receiver sight.