You have to understand that film speeds are not set in stone. With black & white there is a general rule of "exposing for the shadows and developing for the highlights", quite the opposite of colour tranny.
Setting you meter to approx one third slower.....i.e. re-rate 400asa black & white to 320asa and you will get better results. The developer used makes a difference too, for instance if I was using a "speed increasing developer like Microphen, I'd re-rate the 400asa film to 650asa and develop as though I'd exposed at 800asa.
These days camera meters are calibrated to suit colour film. I find older cameras like my Nikon FM and Nikkormat with centre weighted metering give more accurate exposures with black & white, than my current electronic Nikons. This is because they were designed in the days when black & white was the norm.
i started a thread a few months ago about using certain films in certain cameras for this very reason. I noticed that most of my modern film cameras, F5, N80 and N90 performed best with slide film and worst with B&W. but my FA and FE2 gave their best images with B&W. so it could be that Nikon calibrated (would that be the proper term to use) their meters or the camera to work best with the popular film of the time. I absolutely think that the color meter in the F5 gives amazing results with slides, better than any of my non color metered cameras.