What's your reasoning? Longer OAL? If so get a Valkyrie.
A large frame 223 would mean proprietary parts that wouldn't make sense to produce. At minimum you'd need magazines and a bolt, and then hope it's going to feed. Functioning that large of a BCG may also be an issues unless you mount a CO2 tank on it to run the action. At that point you have a bigger heavier rifle shooting the same weak sauce round.
It would be as disproportionate as A cups on a fat chick.
It would be like a male pornstar with a micro penis.
It would be like using a honda civic to build a drag car.
It would be like getting a 22LR conversion kit for you Barrett M107.
It would be like putting a counter sniper scope on said Barrett M107.
For some ideas, it's best to lay down quietly until they go away.