Factual error: The old percussion double barrel shotgun is firing modern shotgun shells, which would never work or fit in that gun, and furthermore are also made of plastic, wrong for the era.
Factual error: The Corvette owned by Bentwood is not a Z06 as shown in the movie. It is a 2014 C7 Stingray and can be identified by the Stingray logo on the side of the car.
Factual error: SPOILERS! While the ending of Al being arrested for murder at his own wedding is dramatic and cathartic, it wouldn't have happened that way. There's no way that the cops would have known to search the wooded area near the cabin; they would have needed to find physical evidence linking the cabin to Al; they would have needed to establish that Al had no alibi for the time in question; etc. None of that would have happened that quickly or that quietly.
Factual error: The Blackledges' car has a license plate that starts with 34. Montana uses the first two numbers on their plates to identify the county that the driver lives in. 34 is the number for Sheridan County which is in northeastern Montana where there are no mountains in sight, but the Blackledge ranch is set near the foothills of a mountain range as you would see in western Montana.
Factual error: The USMC Embassy Guard is an enlisted Marine Sgt. He is wearing a Commissioned USMC Officer's cover (hat) that has gold braid and gold oak leaf motifs on the visor. (01:20:15)
Factual error: While on the fishing boat, the flag flown has 50 stars, while the movie is set in 1941. The US didn't have 50 states, and thus that flag, until 1959. (00:30:08)
Factual error: It is later revealed that Detective Banks partner faked his death by killing a meth-head junkie with the same tattoo as him. He included the junky's filleted skin with the same tattoo in a box with his badge to make it look like the other kills. Police, firefighters, first responders all provide DNA into a data bank to be identified in case something tragic happens and their remains are recovered. William Schenk's DNA would not have matched that of what was in the box.
Suggested correction: William knows that the cops will find out that he's not really dead one way or another. After all, he literally confronts Zeke and reveals he's still alive, knowing there's a good chance Zeke wouldn't take his offer to join him. All he's really doing is throwing off the cops and buying himself a few days when they think he's dead. (Since it can take a few days for DNA analysis to happen.) By the time they figure out he's not dead, he'll have already finished his game and disappeared. Which is ultimately what happens... he finishes his final game with Zeke and Marcus, then gets away.
Factual error: When "some Frida Kahlo-looking asshole" is chasing Harley across the bridge during her close-up you can see that the cartridges are loaded backwards into the cylinder. (00:54:05)
Factual error: Apex, played by Robert Maillet (a retired professional wrestler 6'11" and 350 pounds), forcefully slams Becky (played by 5' tall fifteen-year-old Lulu Wilson who probably weighs under 100 pounds) horizontally with her back hitting the ground from waist-high yet Becky is able to get up with no incapacitating injury that would be expected. Becky also manages to brutally kill him (as well as the three other neo-Nazis).
Factual error: When Armando fired the M141 SMAW-D from the helo, there was no back blast out of the other side, not to mention the other man is the back would have maybe had his face blown off from the back blast also. (01:20:10)
Factual error: It would not be possible for Kyle to see the woman breast-feeding - and certainly not as shown. Kyle was driving an SUV in the left lane and Swin was the front-seat passenger. When a car was approaching the SUV from the right-hand lane and the rear passenger area was approximately side-by-side at the SUV's passenger window (which is DARK-TINTED!), Swin looked toward the car, but his face was right in front of the frame around the windows - he would, at most, see the woman's left shoulder... and the baby was feeding "on the right." I doubt Kyle would have been able to see any part of the woman when he turned his head to look. At most (and this is unlikely given the height of the SUV), he might have gotten a partial glimpse of the woman's left shoulder and only after the car she was riding in was in front of the SUV's windshield (but still in the right-hand lane). (00:07:20)
Factual error: The film consistently mistakes Absinthe ban with Thujone ban. The United States Food and Drug Administration (US FDA) lifted the ban on Absinthe in 2007, 13 years before the events of this film. Thujone is still banned, and Absinthe products must contain less than 10 mg/kg Thujone content.
Factual error: TV reporters said "home invasions" and mentioned trying to find the people who were responsible for the "70 robberies." Lance (in prison), was talking to a woman who was going to write a book and told her he got "twelve years" for "fifteen counts of robbery and vandalism." The crime Lance and the rest of the group were committing fits the legal definition of "burglary" in Illinois (basically, entering an occupied structure with the intent to commit a felony or theft inside; the structure does not have to be occupied at the time of the act). Because there happened to be someone at home during their last (intended) "burglary", this offense would be classified as a "robbery."