The inhomogeneous broadening theory of Portis is extended to obtain equations for the line shapes, signal amplitudes and mode admixtures for nuclear magnetic resonance experiments on bulk ferromagnetic metals. The results of an experimental study of bulk nickel are in agreement with this theory. From the rf power broadening of the dispersion line shape admixed into the absorption signal a temperature-independent rf enhancement factor of order 32000 was observed between 201 and 348K. Allowing for the distribution of enhancement factors at different positions in the sample this corresponds to a maximum value of about 160000. It is shown that domain wall pinning is probably the main limitation to the domain wall motion