According to the movie's script doctor William Goldman, Clint Eastwood, Robert Redford and Harrison Ford passed on the movie. These men would have fit the literary Bob Lee Swagger's age a bit more closely than 'Mark Wahlberg' (born in 1971); Stephen Hunter introduced Swagger as a Vietnam veteran in a 1993 novel taking place in 1992. However, to accommodate Wahlberg's age, this film has Swagger active in Africa in the 1990's instead of Vietnam in the 1970's.
Athens, Tennessee, the residence of the firearms expert Swagger and Nick visited, was the location of the "Battle of Athens" where in 1946 armed citizens removed the corrupt local government and restored free elections.
During the mountain top confrontation, Swagger kills one of the snipers by shooting the counter-sniper through his rifle scope. This is likely based upon an infamous kill by renowned U.S. Marine Corps Gunnery Sgt. Carlos Hathcock during the Vietnam War.
The website that Memphis is given a link to in the chat room, precisionremotes.com, is real. It is the website of Precision Remotes, a Richmond, California company that designs and manufactures remote-operated weapon and surveillance platforms, such as the one featured in the film.
The large caliber rifle that Swagger owns and is framed with is a Cheyenne Tactical M200 Intervention. It fires a .408 caliber projectile accurately out to and beyond 2000 meters. The CheyTac M200 is also available with a Long Range Rifle System, which consists of a laser range finder, magnifying scope with night vision capability, and a weather-sensing module, all of which interface with a PDA running ballistics calculation software.
The dog featured in the film as Bob Lee Swagger's companion was trained by owner Drew Thompson. The dog's real name is Logan. He is a Bernese Mountain and English Mastiff X. Drew states that "he is easily the smartest dog I have ever trained".
In the scene after Sarah Fenn first talks to Nick Memphis, Bob Lee Swagger (Mark Wahlberg) is seen standing outside with a Philadelphia Eagles hat and jacket on. Wahlberg plays for the Eagles in the movie Invincible (2006).
The trivia item below may give away important plot points.
The ranch shootout scene was scaled back due to the violence. Originally, the scene in which Bob Lee Swagger ('Mark Wahlberg') kills a bodyguard with a knife to the throat was scaled back tremendously. Originally, the knife was supposed to exit through his nose, causing blood to spray on Swagger. The scene was cut not because the MPAA deemed the scene too brutal.