Furthermore, lighter grenades and exploding anti-materiel bullets have been introduced since. These developments have occurred without any objection. The military manuals or statements of several States consider only the anti-personnel use of such projectiles to be prohibited or only if they are designed to explode upon impact with the human body. - ICRC
I see where you are reading on the international legality, but the US and other nations looking at smart rounds weren’t terribly concerned on the legal front. The OICW was canceled because a combo rifle and smart launcher weapon was simply too awkward to be practical. That’s why it was split into two different weapons. Once the launcher was stand alone there was no reason not to increase the yield.
https://en.m.wikipedia.org/wiki/XM29_OICW
20mm, think the Geneva guidelines said anything sub 1inch counts as a bullet and can’t explode.
I see where you are reading on the international legality, but the US and other nations looking at smart rounds weren’t terribly concerned on the legal front. The OICW was canceled because a combo rifle and smart launcher weapon was simply too awkward to be practical. That’s why it was split into two different weapons. Once the launcher was stand alone there was no reason not to increase the yield.