The thickest part of the skull is the forehead.  A handgun round, even from a submachine gun, may not penetrate.  If you need a head shot because the threat has body armor or cover.  Make sure it counts.

 

Image from medicinenet.com

 

A gunshot wound to the head with a rifle or handgun will not produce an easily predictable outcome.  The skull is a sealed container that protects the brain. It is designed to block blunt trauma and the curved spherical structure is strong and handles shock very well.  There is very little room for movement.  If the brain swells inside the skull, the pressure can build and cause extensive damage. 
Penetrating trauma (where the bullet gets inside the skull) leaves a permanent cavity (bullet track) may be large, but the damage from the temporary cavity caused by hydro static shock can be much worse. With no room to move, the shock waves can do massive damage.
For some lucky people, the bullet may not enter the skull.  Even if it does, the bullet may pass through non-critical parts of the  brain and survival is possible.
Here a police booking photo booking photo of one of life’s lottery winners:

 

Man accused of killing wife is still in jail Published on Wednesday, Jan 21, 2009 Beacon Journal staff report The man accused of shooting his estranged wife and holding their son hostage from police remains jailed. Daniel Tice, 32, appeared in Akron Municipal Court Tuesday morning still showing the gunshot wound that ended an eight-hour standoff with police this month. He is charged with aggravated murder in the shooting death of his wife, Brandi Tice, 28. Daniel Tice was shot by police once in the forehead while he was holed up in the basement of his Martha Avenue home. The shot fractured his skull. Tice underwent surgery at Akron City Hospital and was taken Friday to the Summit County Jail, where he is being held in lieu of a $1 million bond set by visiting Judge Michael McNulty. Family members say Tice was angered over his wife’s affair with a family member and her demand for a divorce. He is accused of shooting his wife in the living room, taking his son and holding police at bay for eight hours. His 4-year-old son was not harmed. The couple’s two daughters, 8 and 7, were kept from the home when they returned from school. SWAT members worked their way inside the home and shot Tice with an 9mm MP-5 submachine gun after failing to subdue the 6-foot-1, 280-pound man with nonlethal bean bags fired from a gun.

There are big holes and thin spots in the skull.  Use them…based on this guy’s photo, I’m thinking he may have had an extra-thick skull anyway.  If we posted this guys hit on a paper target, the assumption would be that it was incapacitating.  The reason TV and movie head shots go to the forehead has more to do with make up than anatomy.

To instantly incapacitate, you need to damage the brain stem.  This structure is very small and difficult to hit.  A rifle bullet with sufficient energy will open the cranial vault.  Even with a rifle, there needs to be a solid hit.  The outside of the skull will deflect and divert a peripheral hit.

Police hostage rescue

There is no miracle technique or magic bullet.  If you have to respond to protect yourself or others, you will be as good as your training.  Don’t ever assume any one shot or technique will be a fight stopper.  You may get a nasty surprise.

If you have a shotgun, you may have better results.

Another citizen saved.