When major Marcus Reno begins the attack, he draws his revolver. Seconds after, he draws the revolver again.
The screen caption shown at the beginning of the outdoor dance sequence at Fort Lincoln states that the time is the summer of 1876. That event would actually have taken place during the spring, weeks or months before the June 25th battle at the Little Bighhorn River.
Custer's sister Margaret was not married to Lt. William W. Cook, but to another 7th Cavalry officer, Lt James Calhoun.
While in a tent on the plains with his wife Libby, Custer complains to her that he is 'only a colonel'. In fact, Custer was a lieutenant colonel (LC) at the time, and should have used that complete rank title in this conversation. Although the one word 'colonel' may be used informally to denote an LC, in this case Custer's complaint was specifically directed at his actual rank, so he should have used its full title. (Incidentally, Custer had reached the temporary rank of major general during the Civil War. But like many general officers of that conflict, he reverted to a lower permanent rank after the war ended. It is out of respect for his former higher rank that several fellow 7th Cavalry troopers in the movie address him as 'general').
During the Indian attack on Major Reno's positions, the frontal camera views of Reno firing his revolver clearly show its cylinder to be empty. Also, none of the soldiers' revolvers recoil ("jump") when they are fired.
One of the buffalo hunted by Custer is sporting a red ear tag.
When the reporter is taking notes while Custer and his scout Rivers describe the Kidder massacre site, the newsman is using a modern-day small legal pad.
The Grand Teton mountains are shown several times in the movie as being in close proximity to the action. In fact, these mountains are in western Wyoming, several hundred miles from southeastern Montana.
The battle of the Washita River was in Western Oklahoma, a relative flat to hilly area. While snow there is common in winter, establishment shot shows Mount Moran which is in Grand Teton National Park, Wyoming, several states away up in the Northwest.
In private conversations with President Grant, Phil Sheridan calls him by his first name Ulysses. In fact, Grant disliked this name and his close associates usually addressed him by the nickname of Sam.
Some 7th Cavalry troopers are shown with hairstyles from the late 1980s or early 1990s.