S&B 7.62x39 ammunition is no longer imported into the US. If someone knows of a source for it, please let me know. None of the usual S&B retailers have had any in stock for over six months now.
Also, S&B 7.62x39 is steel cased, Berdan primed. It is roughly equivalent to Barnaul 123gr FMJ.
I recommend Lapua ammunition in this caliber. Winchester USA and Remington UMC are relatively economical, brass cased alternatives. I would save shooting large quantities of steel cased ammo for an AKM or SKS.