Factual error: The guns Tuco and Blondie use appear to be 1851 Colt Navy because they have octagonal barrels and the loading ram below the barrel. 2 problems are that 1) the '51 was only made in .36 calibre. When shown from the business end the muzzles appear to be much larger. Colt '61 / '60 came in .44 caliber, but they had round barrels. 2) More importantly they are using brass cartridges to load. Conversions for those pistols to load cartridges did not exist till after the war and these were cap 'n' ball only then.
Continuity mistake: When Tuco pulls the corporal from train they fall down a steep grade. When train runs over the corporal, they're on flat ground. The corporal would be too heavy for Tuco to carry far enough for the ground to flatten out. Watch the ground when the train approaches before the jump. (01:54:55 - 01:56:07)
Factual error: While cleaning his pistol Eastwood is using a plastic bore brush, not available in that era. (00:43:20 - 00:50:00)
Factual error: The movie depicts General Sibley's New Mexico campaign. This occurred in the first half of 1862, with the last battle occurring on June 1, prior to a Confederate retreat to Texas. General Sibley is seen, and he lost his battlefield command altogether in 1863. However, Angel Eyes makes reference to Andersonville prison, which did not open until 1864. The question is also begged as to how Arch Stanton, who died in February of 1862, had completely rotted away by May in dry soil.
Continuity mistake: A dirty Union cavalry officer hits himself to clean off the dust that made him appeared Confederate. His first two strikes barely shake the dust on his uniform, yet, after a cutaway and two off-screen strikes, his arm is almost completely free of dust. (01:31:05)
Factual error: Regarding the train scenes when Tuco is taken then escapes from Mario Brega, there were no trains / railways in New Mexico in any of the years of the US Civil War, let alone 1862 when Selby's short-lived and daft campaign was limited to. I believe the RRs were starting to move into Texas then, but not NM until the 1870s. Also, the whole geography of the film is wrong if the gold was intercepted but 'escaped' with the three people in the wagon near Glorietta Pass in early 1862. The sequence of events means all involved had to go up and down the Rio Bravo constantly - eg. the 'jornado del muerto' is hundreds of miles from Glorietta. This is too complicated to summarise here, but check the actual battles and timelines.
Factual error: Extended version. After finding a dying Bill Carson, Tuco arrives at an outpost looking for a hospital. It's night, or at least dark outside - he is told the hospital is 18 miles away. In the next scene he arrives at the hospital at nearly high noon. A horse canters and gallops (full speed) between 4-30 mph. Basically the hospital was an hour away. (01:14:50)
Revealing mistake: When Tuco is about to shoot Blondie in the desert, and the Army wagon is seen approaching, the driver can be seen sitting far back in the rear of the coach wearing a hat. (01:06:33)
Answer: There's a show called "Hollywood Weapons: Fact or Fiction" which dealt with this exact question (s01e03). Blondie is roughly 200 yds away. In the show the host didn't hit the rope, but only missed by an inch on his first attempt. I definitely think an expert Sharps Rifle shooter could make the shot. The issue however, is the bullet would most likely not actually slice the rope apart as seen in the film (they fired the Sharps at point blank and the rope remained partially intact still). They also tested shooting a hat off someone and (as expected) the bullet just goes right through the hat without lifting the hat at all.
Bishop73
That was another thing that puzzled me. On several occasions in this film, Tuco is suspended from a rope, and Blondie cuts the rope by firing a bullet at it, (I think Clint Eastwood repeated the trick in "The Outlaw Josey Wales"). But if you fired a bullet at a rope holding a (rather large) person like Tuco (or a similarly heavy weight), even at close range, would it really sever the rope? I will have to look out for "Hollywood Weapons Fact Or Fiction." I hope they only used a dummy or a model to re-create the shooting feats. I don't think I would have liked to have been hanging on a rope while somebody fired bullets at me to see if this would sever the rope, or to stand there while they fired bullets into my hat to see if they could lift it off my head.
Rob Halliday