The only problem i have with the 7.62x39 is the steel cases. These can be hard on chambers and extraction with steel cases and not a big choice in brass. Would never pick the 30 carbine . Limited choice and a blisterering mussel blast. Also limited use other than pinking. Why not get a 223 with the 15" barrel. You would have a affordable plinker and a pistol that can shoot to 200+ yards. If a 30 carbine load is viable then maybe a 9mm If avalible could be a choice. +p or +p+ military ammo is very hot and a longer barrel you up fps to near the 30 carbine loads.