As William and Lewis go into their first battle, neither their commanders nor the rebels' commanders have their men fix bayonets. Consequently, as the two lines charge each other, then mingle, they just go by each other, and never engage each other. In reality, at the start of a battle, each side would have fixed bayonets, and when they charged each other, they would have engaged in hand to hand combat using their bayonets. But not fixing bayonets was/is a safety precaution used by reenactors to ensure that there will be no accidents, a tact obviously employed by the producers of this film.
As William and Lewis go into their first battle, the camera pans over the men in their line. One can see that the men have a mixture of Springfield and Enfield muskets. As this is all of these men's first battle, as they are all from the same state, and probably the same community, they all would have enlisted at the same time to form their regiment. Therefore, they would have all been equipped at the same time and with the same equipment, including their muskets (in this case either Springfields or Enfields). But if the film is utilizing reenactors, who are the ones who outfit themselves in the practice their hobby (resulting with reenactors who have randomly chosen to purchase either a Springfield or an Enfield musket) then the soldiers who end up in the film will have quite an eclectic collection of muskets.
This is an entry for an anachronism of a term: "Grayback." The slave catcher finds William alone by the fire and interrogates him about the runaways for which he is looking. He shows him a wanted poster for Kitch and calls him an "ape" and "grayback." As he calls him an "ape" his reference to "grayback" must be to a gorilla, of which distinguished males are called "silver backs." But gorillas had only been "discovered" in the late 1850s, and few outside of the scientific community would have been aware of this discovery. Further, studies and the subsequent discovery of silverbacks would not be made until the early 20th Century, well after the setting of this film.
The slave catcher has 4 escaped slaves at his mercy. He baits three to try to cross the river to freedom, then has them shot while in the river. This slave catcher is obviously driven by greed yet sacrifices the bounty on these three escaped slaves.
The slave catcher finds William alone by the fire and interrogates him about the runaways for which he is looking. He shows him a wanted poster for Kitch, calling him a "grayback." But "grayback" is a term for a Confederate, something this character would not call an escaped slave.
When the slave catcher puts his revolver into William's hand, telling him to shoot Kitch, William would have known that there was not a live round in the gun. This was an 1860 Colt Army, a percussion cap revolver. This was an open frame revolver, meaning that there was no top strap over the cylinder. All it would require to know that this weapon was not armed was a quick glance once the hammer was drawn back. Doing so would expose a bright copper percussion cap on the nipple of the chamber that was to be fired. If the percussion cap was there, then the person holding the pistol would know his weapon was ready to fire. BUT if there was NO percussion cap on the nipple of that top chamber, then even if loaded, it could NOT, would NOT fire. William was a product of the mid-19th Century and trained by the Army to use a percussion rifled musket. He would know the weapons of his time and how they were primed. Therefore, this character would have known this pistol was NOT primed, not armed and would NOT have been fooled by the slave catcher into making the mistake that he made.