Based on his recent work I'd say it's probably 700 pages long and consists mostly of irrelevant backstory.
8000 words, pretty short.
I do applaud him for this, though:
In the 1970s, he published a novel called “Rage” under the pseudonym Richard Bachman. It told the story of a high school kid who takes a gun to school, shoots his Algebra teacher and holds a class hostage. “Rage” sold only a few thousand copies, but starting in the late 1980s, King began to hear about teenage boys who were inspired by the book to commit similar crimes in their own schools. He does not think that his novel “caused” these young men to kill, but he says, “I saw ‘Rage’ as a possible accelerant.” In response, he demanded that his publisher pull the book from publication.
He put his money where his mouth was, despite still being "Richard Bachman" rather than Steven King, and probably making next to nothing at the time and needing the royalties of all his titles.
I don't agree with the notion that fictional ideas subliminally inspire true horror, but if he believes it then he took a principled stand and that's honorable.
That being said, the man knows jack-$#!+ about guns and has written about .44magnum automatic Rugers, which we know are nonsensical. He's not an authority on firearms and probably talking out of his @$$.