The 7.62x39 does not feed well through a AR15 unless it is specifically designed for it. It has to do with the extreme taper of the case as much as anything. If you don't want a can, forget about the .300 Blackout. Ballistically, it is worse than the Russian.

I don't understand your dislike of the 5.56 AR. A couple of 30rd mags full of hard bullets like Barnes or any other deer worthy bullet would work well while waiting for the cavalry. A 1-4 scope with a illuminated reticle would be perfect for non-gun types.