New project? a grendel-cousin?

[Lemonaid]

grayfox, my understanding is that when Ruger made it's Mini 30 they used .308 barrels. You could still use .310 7.62x39 ammo as it would swage down the bullet. A lot more choices of .308 bullets than .310 so I would go the .308 route.
This looked like a fun project. http://bulletin.accurateshooter.com/2013...-and-ammo/
or this.
http://bulletin.accurateshooter.com/2013...s-300-blk/