That jaw from your vice looks like a bad iron casting. When a casting cools off unevenely usualy the carbon in the iron segregates to the side. When you view the two pcs one side will be black and the other side white. Is that the case with your part ? Yrs ago my fathers Redding reloading press bail snapped one side and had that condition. Redding agreed it was a chilled casting and replaced it.

El Lobo