Quote Originally Posted by Firn View Post
A 25x40mm grenade should weight only around a third of a 40x46mm or something like 80 g instead of 230 g.
So how effective can such a small grenade really be, assuming it will air-burst a few metres away from the target? I assume an advantage of this air-burst over the 40 mm is that no energy is lost in the ground. Or, come to think of it, into the back wall of a room after firing it through a window.

Also from Firn:

So it covers quite some needs.
I'm not sure that all the examples you gave can really be seen as needs. Some seem more of a justification to help warrant it's existence. For instance, a buckshot or flechette round seems to me a heavy, bulky and expensive alternative to 5.56 or 7.62. A breaching round however could have merrit.