My friend shot a very big Mulie buck head on many moons ago. He was using a .300 Win Mag and the original 200gr X bullet. The buck drop on the spot and the bullet was recovered under the hide behind the ham.
I don't think anything other than a CNS hit will give you 100% drop on the spot. On the other hand sometimes they drop right there from a lung shot. Animals are funny that way.
I think your 250 yard tracking job has mostly to do with missing the heart, and possibly the lungs too. Just a little different shot placement and your tracking job will be much shorter, imo.
