Just curious...
Unless you already have a substantial investment in the .30 Russian short (7.62x39mm), Or you are going to a place where that is the only commonly available round, I have to wonder, why bother with that particular round??
In power, it is slightly below the hoary old .30-30 Winchester, though it has a flatter trajectory, allowing relatively easy use out to 300yds or so. Many, MANY other rounds out perform the 7.62x39mm at both close and far distances.
And several of those rounds are available in various semi auto designs.
Most of the surplus ammo is not high quality stuff, and neither are MOST of the common rifles in that caliber.
I do get a kick out of the "if you are going to war" questions though. Lots of answers, though few are well thought out. Face it, if you (or I) as a private citizen are "going to war", then there are essentially only two choices, use what you already have, no matter what it is, or join with one side, or the other, and use whatever they will give you.
And speaking of that, its very likely that in a collapse of order situation (and that's what a combat zone is), the people who already have arms and ammo (like the military) are NOT going to share it with you.
In fact, tis likely that if you ask them for some, they will take away whatever it is you already have. (its called security)
SO, if you are in combat, and on your own, your only real option for resupply is whatever you can pick up on the battlefield (without being killed), which means the using the weapons, caliber and equipment of one side, or the other.
Enjoy all the exotics, as a civilian, but realize that if you "go to war" (or it comes to you) all you can really count on is what you ALREADY HAVE.