Q: How do I calculate the actual break force or yield of a bolt for a particular size?
A: The Ultimate Tensile properties for a material like Hastelloy C276 is independent of the size of the bolt, as its based on the x-sectional area of the bolt which typically is 105ksi (at room temp).
However if you are worried about if a bolt will perform in a given application you should focus on the yield strength. This is the measure that really matters which is about 49ksi (at room temp) for Hastelloy C276.
Now to find the actual break or yield force for a given bolt size, just multiply the Ultimate Tensile or the Yield by the cross sectional area of the bolt. That will give you the actual force to failure.