[Tony Williams]

Originally Posted by Rob Philips

I agree that equasions with rate of fire, muzzle velocity and energy content shall lead to conclusions that were already nicely summarized by Tony. I do not agree with his proposed calculation of explosive energies, that rather simplifies the matter, but would agree that a more elaborate calculation would probably lead to the same or similar results in a table with comparative data.

If you look at the final section of my armament effectiveness article, you will see that Henning Ruch suggested a more scientific calculation for chemical energy and the results are tabulated: but this made very little difference to the relative power scores, except to magnify the effectiveness of high-capacity HE shells.

In any case, I'm not finding pattern density, or dispersion, anywhere in these considerations. It strikes me that this could be a flaw, that is not present in the world of hunting shell ballistics. Note that "dispersion" has a negative ring to it, as in "deviation from the perfect line". That would be valid at the target practice range, but it might be a desirable feature in aerial combat.

Pattern density is partly a function of the harmonisation arrangements, but equally so a function of the combined rates of fire of the armament: which also affects the overall armament effectiveness scores in Table 3 of that article.

The harmonisation arrangements are also affectd by the destructiveness of each hit: the less powerful your ammo, the more important it is to concentrate its fire to achieve acceptable effectiveness. So the RAF had to reduce the harmonisation distance - in other words, tighten the pattern - for its 8x .303 fighters during the BoB, but considered increasing the dispersion of Hispano armament, because only a few hits were needed for a kill.

In aerial combat things would be different, as the target is moving fast, in four dimensions. Multiple hits at the same spot with non-explosive rounds could accumulate the damage done. If not at the same spot, which is very unlikely anyway at regular firing ranges, then multiple hits close together could lead to a greater net effect than can be calculated as the sum of the effects of all hits.

Multiple hits on the same spot are highly improbable, even with a high pattern density. All you have to do is look at camera gun film of ground attack strafing runs, where you can see (especially against naval craft) the shots scattered all around the craft or vehicle, due to the movement and vibration of the plane, aim wander, and the dispersion of each gun. Then add to that the fact the aircraft are moving far more quickly than naval craft or vehicles, and the chances of concentrated hits go down sharply.

There was only one way to ensure a close grouping of hits - and that was to get very, very close before opening fire. And by that I mean 50 metres or less. Not many pilots were capable of that.