Shorter shells of the same caliber would withstand higher velocities better, wouldn't they? (both due to the different dimensions -and particularly shorter overall straight-walled section- and the fact that the lower mass alone would allow for a velocity increase with a similar powder charge, though you'd really want a combination of shorter projectile and increased powder charge -which is more or less what the ADEN round did compared to the MK 108, with rather similar external dimensions and overall length of assembled cartridge, but a larger portion used by the case and propellant combined with a shorter, lighter projectile)
I'd think that more conical, tapered shells would be stronger on top of having superior ballistics. (plus they usually used more compact, lighter fuses and put less of the weight at the front of the projectile)