Ts black mountain magnum sight replacement
 

I jeust bought a muzzleloader and would like te change it to a peep/ghost the ones i found say octagon barrel will it still work on the rear mount looks the same to me

Isn't the Black Mountain Magnum made by Thompson Center a round barrel? Mine is. Go to Tru Glow Sights or Williams Sight and see what they have that fits the rile you want to convert. Will an octagon peep fit it ... I really am not sure?

If you're talking about the T/C tang sight it should work. I have one on one of my NewEnglanders. Works great as a "ghost ring" when I use the shotgun barrel for turkey hunting, just remove the aperture.