If you watch any movie on youtube that involves firearms of any description, then read the Comments, you will learn far more about the engineering, manufacture, marketing, sales, and general history of firearms than you will ever want to know - spotted anachronisms being the prompt for the foregoing.

But, sticking to youtube, the Most Unlikely Spotted Anachronism goes to the poster who pointed out that the model of screw holding the hinges to the door did not come into production until ten years after the year the movie was set in. (Can't give you the title of the movie; in fact, that curious criticism is all that I remember about it, other than it was a Western.)