Emilio Estevez was very depressed throughout the shoot because he had recently broken up with his girlfriend. One night, Lou Diamond Phillips decided to play a prank on him in an effort to cheer him up. Phillips had the wardrobe department put make-up on a sheep, dress it up, and put in Emilio's room.
Like virtually all movies about the events surrounding the Lincoln County War, John Tunstall is depicted as an older, sophisticated man. Tunstall was 24 when he was murdered, younger than most of the Regulators. Josiah "Doc" Scurlock was 31 at the time of Tunstall's murder, and Richard "Dick" Brewer was 27. Only 20-year-old Billy the Kid was younger.
Charlie Sheen was reportedly a terrible horse rider. He couldn't keep his balance on the horse and fell off several times. His horse took off after the shoot-out with Henry Hill, and he had no clue how to make it stop.
Lou Diamond Phillips stated in the commentary that he went to a meeting with the producers for what he thought was an audition. After explaining his character to him, he had thought they wanted him to act out a scene. After an odd pause, Executive Producer and Screenwriter John Fusco said "well?" Phillips realized this wasn't an audition, but they were offering him the part of Chavez.
When Colonel Nathan Dudley arrives at the siege of the McSween house with a detachment of cavalry, the troopers are correctly portrayed by African-Americans. The U.S. Army was segregated at the time. New Mexico was policed by the 9th U.S. Cavalry, a unit composed of black soldiers under the command of white commissioned officers and black non-commissioned officers.
When the men are going through the Indian village, "Doc" is in the front of the group, with a cover on his face. It's a stand-in for Kiefer Sutherland, who had left the set that morning due to the birth of his child.
In one scene, Billy reads a report that claims he is a lefty, and replies, "I ain't left-handed." This is a reference to films, books, and media wrongly claiming Billy the Kid was left-handed based on a tintype photograph of him. Tintypes produce a reversed image, making Billy look like he used his left hand to shoot.
When Billy has Doc write a letter to the Governor, Emilio Estevez wanted to make it look like he was making the speech off the top of his head, so the crew made a cue card for him to read. His eyes move while he is reciting the speech.
Dialogue by Casey Siemaszko's character is sampled in the1994 hip-hop song "Regulate" by Warren G. and Nate Dogg,. According to the DVD commentary, Siemaszko had no clue that that had happened, and had never heard of the song.
During the shoot-out at the bar, the ammo blanks were packed with ceramic plaster for a louder sound. While filming the scene pieces of hot plaster were hitting the actors. Emilio Estevez was actually hit in the face, causing filming to stop for a short period while he got checked over. Dermot Mulroney was also shot in the shoulder blade.
A few members of the Hell's Angels Motorcycle Club were used as extras in the bar scene when the group goes to arrest Henry Hill. They were also used as extra security during the shooting of the final battle; that crowds of onlookers were getting too big.
In the final battle preparations, Kiefer Sutherland had to put on a "squib blood pack" vest underneath his clothes. The rig was supposed to be triggered by Sutherland himself by pressing a hidden button. The whole rig took an hour to set up. When it was time to shoot the scene, Sutherland got on his horse and accidentally pressed the trigger, popping all of the blood packs. Setting the rig up again took another hour.
The term Regulators was applied to any private armed security force, usually hired by cattle, oil, or railroad barons. Their primary function was to prevent the theft of their employer's property, but they also served as muscle to enforce their employer's will. They were most often Civil War veterans who either enjoyed that kind of work or had no other marketable skills.
Tom Cruise: the fourth person shot when Charlie bursts out the house shooting. Cruise was on set one day, and the director thought it would be great to get him on the movie. He dressed Cruise as a soldier and filmed the climactic battle.
The trivia items below may give away important plot points.
In real life, "Dirty" Steve Stephens survived the Lincoln County War. He left Lincoln after the conflict, announcing his intention to relocate to Denver, Colorado, then disappeared. His ultimate fate and final resting place remain unknown.
Charlie Bowdre was a real historical figure. In the movie, he dies. In real life, he survived until a gunfight at Stinking Springs, New Mexico that was depicted in Young Guns II (1990). He was laid to rest in the old Fort Sumner Cemetery. Seven months later, Billy the Kid was laid to rest beside him and Tom O'Folliard.
Dick Brewer is shot in the stomach during the shoot-out with Buckshot Roberts. In reality, the top of his head was blown off. Almost everything else about the shoot-out is true, other than Doc being shot in the hand and Roberts taking refuge in an outhouse. In reality, George Coe's finger was shot off, and Roberts (who was gravely wounded by a shot to the gut that started the gunfight) was hiding in a small home.