Hi Tomo,
Muzzle velocity is not a big deal, as you either have a non-manoevring target, which you can shoot at medium ranges with good chances of success regardless of muzzle velocity, or a manoeuvring target, which requires you to close to a very short range anyhow.
If you're closing to short range with a manoeuvring target, it's no longer just range that's a problem, but geometry as well, as you have to achieve a firing solution that you can sustain for a long enough time to actually destroy the target.
If you have a low-velocity cannon capable of destroying a target with a single hit, this problem is actually easier to solve than with a high-velocity gun that requires a lot more hits, as you can achieve the single hit even with a brief firing solution, such as when momentarily pointing the nose at the target, while for a lower-firepower weapon, you are pretty much forced to fly yourself into a position that gives you a sustained tracking shot.
Everything else staying the same, a higher muzzle velocity is obviously preferrably, but realistically, you'd have to make some compromises to build a gun to replace the MK 108, but using the same technology as the MK 108. If you sacrifice shell size to raise muzzle velocity, you might gain a 20% increase in hit probability for a 40% decrease in probability of kill, for example ... that would not be an improvement, overall. If you raise muzzle velocity using the same shells, you might end up decreasing rate of fire while increasing weapon weight ... that's the path from the MK 108 to the MK 103. Again, the original MK 108 was the better weapon for fighters, overall.
Not to say it would impossible to come up with a better 30 mm cannon than the MK 108, but I wouldn't expect any great leap ahead even in the best of cases. In the "post Battle of Britain" context, I would rather try to get the MK 108 into service earlier, instead of risking delaying the introduction of a new cannon by trying to build a different weapon instead.
Regards,
Henning (HoHun)
