Factual error: John Blair rides for the pony express, which operated until October, 1861. However, all of the handguns in the movie are cartridge Colts, which did not come into existence until 1871.
Factual error: This movie takes place post-civil war, and Fisher, in his first discussion with General Cortinas refers to the "Republic of Texas" being ripe for the taking. Texas ceased to be a republic in 1845, when it joined the United States.
Factual error: Charlie Chan claims that mixing hydrochloric acid with ferrocyanide of potassium is mixing two acids. Ferrocyanide of potassium is not an acid. (00:27:00)
Factual error: Two of the little pigs startle the third one who has the gun, and he shoots into the tree, knocking down apples. The weapon appears to be a single-shot blunderbuss with a hammer fire action. He chastises the other two pigs for tricking him and gets up with his weapon to walk away. As he passes them, they blow the horn at him again to scare him a second time, causing him to shoot again. Yet he never reloaded his weapon. The single-shot blunderbuss would not have been able to fire a second time. (00:02:20)