In the 2003 film Runaway jury the plot centers around suing a manufacturer of guns for damages in the shooting.
However, the book centered around suing a tobacco company for damages caused by smoking.
Why was the film changed to gun manufacturers?
The Insider, starring Russell Crowe and directed by Michael Mann, came out in 1999. The film was a huge box office and critical success based on Jeffrey Weigand's experience as a whistleblower in the tobacco industry, winning 7 Oscar nominations and this film would have gone over the same subject again so it was changed to another contentious subject...Guns.
For over six years the courtroom drama — based on the John Grisham book — shuffled through directors from Joel Schumacher to Mike Newell, and leading men from Edward Norton to Will Smith (the latter was nixed by Grisham, who had casting approval). Even the case changed: In the novel, a plaintiff initiates a public-health suit against Big Tobacco. But The Insider smoked the freshness out of that angle, so gun manufacturers are the new target.
The novel's focus on big tobacco was retained until the 1999 film The Insider was released, necessitating a plot change from tobacco to gun companies. Another reason more political, the film came out just a few years after the Columbine shooting so personal attitude against firearms (especially among hollywood) is ubiquitous in movies.