New Army "Caliber Configuration Study"

[stanc]

Less absurdly, the 5.7x28 FM P90 or 4.6x30 HK MP7 are both designed to inflict disabling wounds after penetrating CRISAT body armour at out to 200m, and against soft targets are probably effective (in terms of being able to hit and - potentially - inflict disabling wounds) out to 300m - provided a crosswind isn't blowing. Since I have often been told that it is pointless to expect the average soldier to see or hit a target beyond 300m, that would seem to meet the baseline minimum needs, and the weight saving would be huge.

Indeed it would. Many years ago I contemplated the possibility of combining the guts of the P90 SMG with a 40mm grenade launcher. Very large magazine capacity (50 rounds!), with minimum recoil and maximum full-auto controllability for the close fight, together with high-explosive, fragmentation rounds for long range engagements where bullets have low hit probability.

But, that was when "long range" meant 500 meters or so. Even with improved 40mm grenade rounds having a maximum range of 600-800 meters,* that still wouldn't quite cut it for some of the engagement ranges seen in Afghanistan.

* http://www.quarry.nildram.co.uk/grenades.htm