What I would like to know is how far are these deer running on your friend. This may just be a matter of expectation. The other questions I would have would be: 1) The range at which he was shooting these deer 2) Where he was aiming. 3) Flinch
Most of my deer over the past decade have been taken with either a 30-06 or 35 Whelen from inside 165 yards. Almost all had the tops of their hearts blown off and both lungs pulped. A good number drop on the spot. However, a sizeable number run a bit. I would say that with rare exception, I can stand in the tracks of the deer where I shot it, and see where it went down. It might be 10 yards. It might be 60. I don't see this as a problem.
One thing I noticed with my sons early on was their tendency to subconsciously move their aim towards the center of mass instead of concentrating on the chest. They would swear they'd sent the round towards the boiler room, but they were hitting behind the diaphragm. This is a matter of confidence. The cure was simply getting enough deer under their belts.
I'd also be looking at the 3-dimensional aspect of shot placement. I like taking off the top of the heart, but if the angle is wrong, I might only hit one lung. Now I have a runner on my hands and it might be lost. If your friend is just picking a point on the hide and not considering how the bullet will travel, that will give him the sort of trouble he's having.
