RE: 30-30
The 30/30 is my favorite whitetail weapon. My favorite round is a the 150 gr. Winchester power point. The 150 and 170 gr. are your two choices if you buy store- bought shells.
The only two reasons I see to use the 170 gr. is
1. You might want a little better penetration for something like a tougher skinned feral hog.
2. Your gun might group the 170 gr. better.
Both shoot almost identical in my Marlin, and both have no problem completely penetrating a whitetail.
C. Davis