From today's NYT:
Victims of mass shootings make up about 1 percent of overall gun deaths in the United States, according to federal gun homicide data analyzed by the advocacy group Everytown for Gun Safety. The risk of dying in a mass shooting is even lower in California, the nonpartisan Public Policy Institute of California recently found. Nationally, suicides account for just over half of all gun deaths.
Note: To be thorough, I oughta check out the credentials of two organizations cited above. I did not because I thought if anything the Times would have used the least conservative numbers. The data on suicides came from the Kaiser Family Foundation.
It makes sense, which is my usual rule in looking at statistics.