Laser-Guided 40mm Grenade

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Look at the slightly darker section that wnds about where the guy' left thumb is. That section is about the size of the payload section of the standard 40mm HE round. Indeed the payload might be in that dark section just behind the fins.

The rest is likely to be batteries and electronics even though I am surprised that much room is needed given how compact the guidance module could be and the short duration of guided flight.

The dark section aft of the fins appears to be a rimmed "cartridge casing" to me. I'd suspect it uses a high-to-low pressure propulsion system (similar to the regular 38 blank in a '203) to expell the round from the launcher before the rocket motor ignites. Kind of like the kicker charge in an RPG or a Javelin, etc...

I think you're probably right about the darker silver portion forward of the fins being the payload. If so-- They need to do better.LOL Of course it might be a kind of placeholder, subject to expansion later in the program. It could take up additional space later as other components are further miniaturized.