7.62x39
I like the x39 threads for deer, as the boy and I both shoot same with a Mini-30 and a M77-II. We have had fine results, but have not shot any with import ammo. Mostly we used my reloads and a 135 gr Sierra SP, no longer mfg'd.
+1 on the import hollow points. My simple water jug tests show them sort of frangible. There are on line videos where some do not open up. Not for me.
There was a very good article done on the Brown Bear 125 gr SP being shot into ballistic gellatin and the results were very favorable. The bullet is not a FMJ/HP hybrid, but appears to be a genuine SP and expands nicely. I felt good enough about it, after reading the article once or twice, that I actually zeroed the Mini-30 for Brown Bear 125 SP, it and hunted it this year, but did not take any shots on those days.
Contrary to others, the 150 slug does not go fast enough to suit me from the x39 ctg. Especially the spitzers, which are intended for higher velocity. Now, the 150 gr FN/RN as for the .30-30 might be an interesting reload.
With a quality slug, the x39 will be plenty for deer, at woods ranges.