>>6867690I just had an idea, if you're dead set on using both Mega and Rockets out of the same barrel without switching, you could just make a two-stage stepped barrel with the smaller Mega size barrel sticking out of a larger Rocket sized barrel.
Or if you're fine with reaming your Mega darts a bit, use a 17/32in brass barrel. Mega darts fit over a little snugly and microdarts obviously fit in it. An omni-launcher barrel.
5 second MS Paint diagram if I don't make sense.