Longest penetration on an expanding bullet? For me? Muzzleloader shot using a T/C Maxi-Hunter, .50 caliber, 470 gr. HP, backed by 100 grs. of 777.
A whitetail doe, about 125 dressed, facing me at about 25 yards took one dead center in the chest. The conical, at a likely impact velocity of 1400 fps, went lengthwise through her, then hit the yearling behind her at a quartering toward angle (yes, I knew the yearling was there, but the quartering toward resulted from a step in the right, er, wrong direction at the shot.). The bullet traversed the yearling from through the front leg bone, diagonally across the chest cavity, and out the opposite side just in front of the off-side hind leg. The only bones hit was the front leg bone and rib or two on the second deer.
HUGE exit wound on the first doe, and the entrance/exit wounds on the yearling were just catastrophic. Also, the legal limit is two-per-day, so having two on the ground instantly was kosher.
I switched to 90 grs. of 777 and the 275 gr. HPs afterward. I don't need THAT much penetration on whitetails.
