I used to know these numbers pretty well, but who knows ... in any event, as memory serves gun deaths are suicide>homicide>accident>self-defense, but that the most likely deadly use of a gun in the US was suicide.
for 2012:
In the U.S. for 2010, there were 31,513 deaths from firearms, distributed as follows by mode of death: Suicide 19,308; Homicide 11,015; Accident 600.
http://library.med.utah.edu/WebPath/TUTORIAL/GUNS/GUNSTAT.html
deadly use in self-defense generally runs about 1% of deadly use.
So, mostly, by far, handguns in the US are used for suicide. As memory serves 5-10% of homicide with guns are "justifiable", but those are pretty stale memories.
PS - I'm not pro-gunning this issue - get rid of the bloody things is where I stand, just pointing out that some correlations are a bit murky.