While planning out the dimensions of the set, Ben Wheatley built a scale replica of the film's warehouse in the video game Minecraft.
Armie Hammer said that police appeared on set during the second day of shooting following calls of concern from members of the public in nearby shops having heard gun shots.
Wheatley described games such as Counter Strike as a source of inspiration for the film.
Ben Wheatley has stated a big reason he set the film in the 70s is so there would be no mobile phones.
Luke Evans was cast as Vernon but dropped out due to schedule conflicts with Beauty and the Beast (2017). The role was reworked for Sharlto Copley when he was cast.
Ben Wheatley has said that one of the inspirations was an actual F.B.I. report on a Miami shootout.
Ben Wheatley wrote the role of Chris for Cillian Murphy after the actor approached him expressed a desire to be cast in one of his films.
Sara Dee features in Free Fire and all previous Ben Wheatley movies he's directed for cinema release. She plays the telephone voice.
Chris is displeased because the weapons are not as "ordered", but "AR70s". In fact the folding stocks identify them as a version made by Beretta for Special Forces use - the SC70.
Brie Larson and Michael Smiley have both worked with Edgar Wright; he directed Larson in Scott Pilgrim Vs The World and he directed Smiley In Spaced and The World's End.
Sharlto Copley and Noah Taylor both star in the online streaming series Powers (2015) as Christian Walker and Johnny Royalle.