I would go with excessive velocity myself. For fun call Swift and get their thoughts on it.

The bullet on the left is 30-06 recovered from a zebra. Bullets in the middle are from my .416 Rigby recovered from wildebeests. The bullet on the right was also from a wildebeest. The shot was a quartering to, bullet entered just behind the shoulder, busted a rib and I assume closed up, before traveling thru the body, breaking the pelvis and ending up in the rear ham.

When hunting water buff my aussie ph told me he was thinking about getting a 458 lott for better penetration than he was sometimes getting with his 458 winnie. He was using woodleigh softs. Although I didn't tell him this I was thinking the greater velocity of the lott would just cause the wide mushrooming woodleighs to expand even quicker and maybe even getting less penetration.