50 caliber muzzleloader

I'm unsure of much about this rifle as my aunt found it in her house after my uncle passed away and had no information about it. It has proof marks and is 50 caliber. It says plainsman on it. It appears to be in nice condition and the bore is nice condition. I'm guessing it is probably from the 70s or 80s. It would be a nice wall hanger or probably a nice hunting rifle.