Alternative airborne guns

[tomo pauk]

This might not be much of an advantage.
For a give stage of fuse development you can't make the fuse lighter so that means you cut the body of shell and the HE capacity more than the 75-76% indicated.
The 30mm mine shell already lost velocity at a pretty alarming rate. A shorter, stumpier projectile will loose velocity even faster so you may not get much, if any, increase in practical range. That is much difference in time of flight to a given/desired range.

330g shell was supposed to loose 130 m/s from a still-standing muzzle to 300 m, as well as having the drop of 2.17m - both at sea level. Let's say, for sake of discussion, that 250 g shell looses the speed at 20% greater rate. That is about 155 m/s loss from muzzle to 300 m. Even if the MV is 600 m/s, that is still a faster shell to cover 300m, with benefits for any aspect of ballistics, thus increasing the hit probability.
Low density air at ETO altitudes where a hard-hitting cannon will lessen the rate of velocity loss.