When Hamer is purchasing weapons in a gun store, a shot showing the inside of the firearms catalogue he is holding clearly shows a German Gewehr 43 semi-automatic rifle at the top of the page, labelled a "G-43." The Gewehr 43 was developed and first manufactured during World War II in 1943, almost a full decade after the pursuit and killing of Bonnie and Clyde in 1934, so it could not have appeared in an American interwar firearms catalogue at the time.
In a scene in a Honky Tonk, there is a guitarist in the band playing a copy of a Selmer-Maccaferri guitar. These instruments were made in Europe, only starting production in 1932. It would be highly unlikely that anyone in Texas during the Depression would have even heard of this guitar let alone owned one.
When Maney turns the car radio on, it starts playing immediately. In the 1930s, radios used vacuum tubes, which must warm up for a few seconds before they will function; hence, the sound would not start instantaneously.
The thug at the bar threatens Maney Gault with an Italian stiletto style switchblade, a knife style that did not appear in the United States until American servicemen stationed in Italy brought them home after WWII. Inexpensive switchblades were widely available in the United States in the 1930s, as modern legal restrictions on these knives were yet to be enacted, but most looked quite different from the one in the film.
In a shot looking upwards at Hamer during the bottle-shooting sequence, contrails can be seen. Airplanes capable of flying high enough to create contrails were extremely rare in 1934 and the few that existed were unlikely to be flying over central Texas.
When the federal agents meet Hamer for the first time, one describes their effort as a "thousand person" force. At the time, the term used would have been a thousand man force. Later in the film, Gault uses the correct term of a thousand man dragnet.
Among the weapons circled in pencil, presumably having been chosen by Hamer, in his firearms catalog while he is purchasing weapons for the pursuit is a pump-action shotgun labeled a "Remington 12 gauge, pump action." Then, while shifting his thumb to point at it as if to remind himself about it Hamer asks for "that Remington Model 11..." However, a Remington Model 11 is a semi-automatic shotgun and visually quite different from the catalog illustration.
One of the weapons Hamer purchases is a BAR (Browning Automatic Rifle). Though the weapons were available on the civilian market they were so prohibitively expensive that the likelihood of their being in a small town gun store is extremely slim.
Bienville Parish Sheriff Henderson Jordan speaks with a distinctly Cajun accent. Due to deeply felt racial and religious prejudices of the time, behaving in a Cajun manner would have disqualified him from becoming Sheriff and would have put him on the margins of Protestant North Louisiana society. Unfortunately, the KKK would have enforced this. Sheriff Jordan, like most people born in North Louisiana, would have sounded much like the Texans.
These accent differences still exist, thankfully without the discrimination.
Several times the phrase "manos arribas" is said, as if "arriba" is an adjective describing the hands. But arriba is an adverb describing the direction of the hands (up) and and cannot be plural. The correct phrase is "manos arriba". However, this is likely an intentional embellishment meant to illustrate Gault's unfamiliarity with the Spanish language.
Thick stands of pine trees appear in numerous scenes set in Dallas and other north central Texas locations. Pines are rare in north central Texas because the predominant alkaline clay soils stifle their growth, but they are common throughout northern Louisiana, where the scenes were filmed.