In general, for single engine planes, I would think that a single one of several hits of small caliber was frequently or even usually the key hit which knocked out a key system or the pilot, rather than some combination of hits accomplishing that when no single one of them would have accomplished it. And then it was probably also common for several different hits to inflict damage sufficient to down the plane without the others, overkill. What would be relatively unusual would be one hit knocking down a plane when it was only hit once altogether, except by fairly large caliber rounds. For bigger multi-engine planes it was probably more common for each of several key hits to be have been necessary to down the plane, because of more redundant systems.Joe