Quick, Im glad to see you added Paco's link!!
Spanky, Quick, your right displacement rules the roost. I am not downing the 30-30, I'm just sticking up for the 7.62x39! It seems the little russian gets a bad rap everywhere. There is so much bad written about it that RD is second guessing his purchase before he has even shot his rifle. Any issue with the 7.62x39 and some are ready to throw it in the scrap heap.
I have been shooting the little russian for a while. I am not an expert reloader by any means but I have found out that it can do alot with a little powder. With a few considerations for it having been designed to chamber and function in autoloading battle rifle, you can load accurate, dependable and versatile ammo for it.
RD, unless you want to shoot milsurp ammo, keep your little 7.62x39 and at least try it out. It won't replace your 30-30, but I have a feeling you might like it. . . I like mine!