As previously mentioned (see Most lethal methods of suicide), whilst using a firearm to commit suicide is one of the most reliable methods, it is not failsafe. Reasons for non-fatal suicide attempts by firearms include attempting to shoot the gun in the chest or abdomen (presumably aiming at the heart) but not hitting the heart, bullets passing through the temples and missing the brain, aiming up through the chin, flinching, thus missing important parts of the brain, not using powerful enough guns or poor ammunition. See the section Reliability for more information.
Chances of a successful suicide attempt would seem to be maximised by:
Using a shotgun rather than a gun or rifle. In his study of gunshot injuries in Mobile Alabama1, Riddick found that of those surviving a firearm suicide attempt, 80% used a handgun, 15% a rifle, and only 5% a shotgun. However, shotguns can be more difficult to aim into the side and back of the head, which are the most fatal points to aim (see below). They do deliver much greater energy at impact though (meaning they can do more damage).
Firing into the head rather than the body. Comparing studies of firearm suicide fatalities2 and non-fatalities3 suggests that there are far fewer survivors with head wounds than chest or abdomen. Aiming into the chest or abdomen and using a hand gun is a worst case combination.
Using a gun that works properly and ammunition that is not old. Sounds obvious, but old ammunition might not reach its proper velocity when fired. A gun not working properly could have a similar effect. Geo Stone4 discusses calibre of gun and type of ammunition at length. He concludes that there is no overwhelming evidence of higher calibre size being more effective, although there is increased possibility that a lower calibre will not penetrate the skull.
He also notes a number of unusual cases of people surviving attempted suicide by firearm to the head involving antique or homemade ammunition. Bullets that mushroom on impact cause more damage than those that don't. For this reason, bullets with full metal jackets (tip of the bullet is metal as well as the case - see http://en.wikipedia.org/wiki/Full_metal_jacket_bullet) should be avoided as they do not expand.
One knowledgeable reader of this website wrote in to suggest that those using a shotgun should consider using shotgun shells that shoot slugs, which is one piece of lead instead of a number of smaller balls of lead. Or else if using shot, to use buckshot, which can come in 0.24 - 0.36 caliber, instead of 0.05 which is used for things like clay pigeon/skeet shooting. The higher the caliber, the bigger the pellets (meaning they better maintain their speed and energy on impact), but the less of them.
For those attempting a suicide aiming at the chest, the heart is target. Deflection by the ribs can be an issue. Stone4 suggests aiming under (or between) the left side ribs, with an upward trajectory toward the right side of the neck. Even if fatal heart damage is not caused, there is a fair chance of fatal results by hitting either the aorta (largest artery) or the vena cava (largest vein), or their major branches.
Using a shotgun if aiming at the chest will also increase the chances of a fatal outcome due to the fact shot spreads out and can cause extensive damage even if not aimed quite correctly.
For those aiming at the head, the most popular site is the right temple2 (the left temple presumably being for left handers), second comes the mouth, followed by the forehead.
Stone mentions that a bullet that that damages the spinal column where it meets the base of the skull (base of the head at the back) tends to be quickly fatal, and this is most likely achieved by aiming slightly down through the mouth, or else simply pointing the gun at the rear base of the head. He speculates that aiming here, with a high energy bullet/shell is the most reliably fatal combination. However, using a shotgun to the temples or through the mouth is likely to be even more effective, using one hand to hold the shotgun in place and the other to pull the trigger.
Shots to the front of the head may simply damage the cerebral cortex which may not be life threatening, so aiming here is inherently more risky unless aimed as such to hit other parts of the brain.
Likewise, shots under the chin are not recommended as people tend to flinch when they pull the trigger, changing the bullet's direction and thus reducing the chances of fatal brain damage.
Read more on firearms as a suicide method by selecting:
And anyone seriously considering firearms as a method of suicide is also advised to see Help me.
L Riddick, "Gunshot injuries in Mobile, Ala.", Am J Forensic Med and Pathology 13 (3), 1993.
JW Eisele, DT Reay, & A Cook "Sites of Suicidal Gunshot Wounds", J Forensic Science 26 (3), July 1981.
RL Frierson and SB Lippman, "Psychiatric Consultation for Patients with self -inflicted Gunshot Wounds" Pschosomatics 31 (winter 1990).
Geo Stone, Suicide and Attempted Suicide, 1999.