Dead Zero, by Stephen Hunter

It appears that I've run into a series.   The hero of this novel, Bob Swagger, is the star of a number of Mr Hunter's books; I've not read any of them before this.    That lack of background caused no harm; this is an excellent thriller.

The hero is a retired military sniper; another hero of this novel is a current military sniper.   There is, consequently, lots of sniper dialog, war scene, blowing things up, and killing.   As a movie, it would get an "R" rating for violence.