A method of deriving the shape of pair potentials describing both the long- and short-wavelength behaviour of b.c.c. metals within the Finnis-Sinclair many-body-potential model is described. The method guarantees a fit to both the elastic constants and zone-boundary vibrational frequencies of b.c.c. metals using the five nearest-neighbour shells in the b.c.c. structure. The application of the method to niobium is briefly discussed and compared with previous work.