You realize how fast a dear can cover 250 yards right? I'd bet at least 2x as fast as a human. Minimum.
If a human can live for 15 seconds without blood flow to the brain, how long do you think a deer can live?
That's NOT bullet failure. That's expiration due to blood loss.
If you want instant kills, then use a bullet designed for that purpose.
If a deer walks or trots for 15 seconds with a blood loss rate of (drops / yard)...it will leave a good blood trail.
If a deer runs at FULL SPEED for 15 seconds with the exact same blood loss rate...it will leave a very difficult blood trail.
The problem is not the bullet. It's what your bullet is designed to do, in relation to where you place it.