No, there's no correlation between protein and calcium % in a feedstuff.
For example, alfalfa is pretty high in protein and also high in
calcium. Soybean meal contains more than twice as much protein as even
extremely rich alfalfa, but only about a third as much calcium.
Straight mineral pre-mixes may contain alot of calcium, but no
protein at all.
There are a few correlations in evaluating feeds, for example, as
protein goes up, generally energy goes up, although not always at the
same rate bewteen different feeds. As fat content goes up, energy
always goes up. And as fiber goes down, generally energy goes up.
There aren't any hard and fast numbers associated with these
correlations (except for the fiber/energy one), they're just for some