I have an uncle that lives, sleeps, eats and breathes the 264 Win Mag. He has killed over 30 elk with it and I lost count of how many mule deer. He has and still uses 140 grain Partitions and Sierra BT and has never had a problem and I have never had to help him track anything.
As for Bergers they are made to break apart and make mush, just like the results you got, and many people use them on elk with great success. The school of thought is that all the bullets energy is transferred to the animal when the bullets does not exit. I am not a fan of that thinking but you'll need to make up your own mind on that.