I have shot the 300 grain QT bullets over 2500 fps. I hit a small deer and only got a few inches of penetration and a wound about 8 inches in diameter! needless to say that was my last usage of them
Now, while I can't PROVE that the pure lead bullets are badly deformed as they leave the muzzle at high velocity, BUT when I was shooting thinly jacketed bullets I had problems and would bet that a lead bullet would deform at even lower velocities!
These pictures are of a 8mm 150 grain Sierra Pro Hunter shot from a custom .50 smokeless ML @ around 3,000 fps.
Virgin bullet and one recovered from a deer. Notice the base expansion.
This shows the shape of the sabot and why the bullet took the shape that it did.
PS these were very accurate, but obviously the BC was drastically altered. I have since switched to an Accubond with its very thick copper base and moved the petal break points to below the bullet base.