The always fun ID this piece game.

[Gordylew]

OK Mil Surp guys. What does this rear sight go to. I was thinking 1873/78 Springfield but I think I'm off.

 

[Gordylew]

Hmmm no idea?, must have the xspurts stumped.

 

[BlackJackAce]

Hard to say but looks like it's missing the slide for elevation adjustment.

 

[JBWJr]

US Springfield Trapdoor Model 1873 Rear Rifle Sight | #75001950​

 

[bulletpaluza]

It's for a remington rolling block.