While I wouldn't want to limit myself to only head shots... I have shot a great many deer in the head over the years but after a shot two years ago I amy not be doing that anymore....
I shot a nice sized doe at about 35-yards with my 243 (yea not a 300 Whisper) and it was a nice standing profile shot so I decided to shoot her in the head so as to not loose any meat. It is the first time I shot a deer in the head that they didn't drop but I hit her in the head just above her lower jaw where the lower jaw connects to her skull.
The deer took off running like she wasn't hit and I sat there in shock as I have made clean kills on groundhogs at 400-yards with the same load and rifle and I knew my POI. Well, I walked over to where she was and the 243 round did it's work as blood and pieces of bone were there to show I didn't mis. I had to track that deer for a good 500-yards or more before I saw her working on getting up and I was able to put a second round in her and dropped her for the count. The original round completely tore the lower jaw off the deer and the bottom of the skull had a good sized chunk out of it. It really was a pathetic looking sight and while the deer would have died soon I didn't like the delay.
Darndest deer I have shot in 20+ years of hunting as I am just not used to shooting a deer in the head and having it take a sigle step much less run 500+ yards and live for about 2+hours while we tried to let it sit and die... And this was with an explosive 100-gr 243 round at very close range. Normally the whole head of the deer would have been gone... I just can't imagine nonexpanding bullets being in my future with a plan to only take head shots... In fact, last year I stuck with heart shots...
Now, Back on topic:
I have never used the 300 Whisper on deer yet but from everything I have read the light single shot pistol bullets are excellent bullets... I am pretty sure I have a box of 125-gr Nosler Ballistic Tips in my reloading stuff as well and if I get to use my little
300 Whisper Bolt-Action AR-15 pistol for deer this fall it would be the bullet that I would be using!