As aweful as it sounds, if you blow that deers guts up or out, it still won't go far. A small hole in the guts it will go a long way. Eventually did a painfully death.

Breaking important bones is also part of stopping vs killing.

Shock. A near brain miss with a more powerful cartridge might stun an elephant. Whereas from a lighter bullet, next to no effect.

Adrenalin plays a big part too. Wounded and angry, harder to put down.