Bob, I assume that you mix up B.C and S.D? The ballistic coefficient has more to do with how streamlined a bullet is, i.e; a round nose allways have a lower B.C than a spitzer, but B.C is allways higher in the smaller diameter bullet, among bullets with the same weight, due to sectional density (S.D)
Heavy 6,5 and 7mm bullets have superior sectional density and therefore exhibit great penetration, thus works surprisingly good even for larger game as moose.

Read more if you google "sectional density", chuckhawks for example.

Thanks,
Nojden