Anyone seen this? Came out a year or two ago I guess. Wolf makes a 278g bimetal bullet in necked up 7.62x39 case and KAK makes barrels pretty cheap. It's to 7.62x39 what basically 300blk is to 5.56... uses 7.62x39 bolt and mags. Pretty interesting... Not much for ammo available yet but who knows?
https://www.thefirearmblog.com/blog/2017/07/07/potd-9x39mm-us/
https://www.thefirearmblog.com/blog/2017/07/07/potd-9x39mm-us/