Actually, there is no mold release on a molded metal item - the temps they are poured at are much too high. With either sand casting or "lost wax" proceedures, the mold is destroyed when the object it contained is removed. Priming was very important when most molded metals were lead or lead alloys. If you didn't prime them, they would corrode beneath the surface paint. Britianna metals don't contain any lead (to my knowledge), and in theory, don't corrode.
Having said that, when working with molded metal items (like figures) because they get handled by you (and quite possiblly the people who packaged the model) and skin oils are on them, I wash them in warm soapy water, let them dry and then prime - The primer also does a fine job of bringing out any defects you might have missed earlier.