Been following this for a while.
I yearn for a shell ejecting m249 or m240.
I don't even care if the bb's are in the shells, they can be in a top magazine like the VFC M249, or there was another one I saw on youtube one which had an internal magazine/hopper in the receiver.
The shells and links would need to be biodegradable & disposable to make it or any shell ejecting RIF viable though... I'm not picking them up!
That said, if one was going to all that effort you'd be aswell inventing a new hobby with caps or something in the shells for feedback and just having lasers on the end of the RIF to do something like the MILES or TES systems.?