Rodd Redwing, a fast-draw artist, was a Technical Advisor and worked with Robert Culp on this movie. Redwing suffered a heart attack on the plane returning from filming in Spain, and died shortly after landing in Los Angeles, California.
Quentin Tarantino has said this movie was one of his inspirations for Kill Bill: Vol. 1 (2003) and Kill Bill: Vol. 2 (2004). "Why I love Hannie Caulder so much is Robert Culp," he said. "He is so magnificent in that movie. I actually think there's a bit of similarity between Sonny Chiba (Shin'ichi Chiba) and Uma Thurman in Kill Bill and Raquel Welch and Robert Culp in Hannie Caulder."
Bailey makes Hannie an English Tranter self-cocking revolver. It was invented by William Tranter (1816-1890) in 1856. As mentioned, this first model had two triggers: the lower one to turn the cylinder and cock the hammer and the other one to fire the weapon. The one in the film appears to be a cap and ball model in 54-bore (.442 caliber). The second version of this pistol had a single trigger like most all double-action revolvers since.