RE: Best caliber for under 100 yards ?
I used to hunt with a 30'06 and a 270 Win.Both of them are permantly retired to the rack,during hunting season,because,now, my shooting range will be limited to 100 yards.My rifle of choice is the same as yours;the 30/30 Win.
If you want a little more Pizzaz,go up to the 300 Savage or the 30/40 Krag.They will give you a little more confidense with moving targets or bad angle targets.
I'm assuming that you re hunting Whitetails.If you are after Moose Elk,etc,then go for the big guns.
Frank