We've all seen the endless parade of film gun goofs. In a similar vein, if one reads enough fictional works, well gun goofs will be encountered. I've seen them in both mainstream, successful authors and more obscure writers.
For example, I recently read the first of the Dirty Harry novels (not novelizations, different stories) and started a second before wandering back to the nonfiction stack. (Oh, they are utter pulp trash, but that is one of the appeals.) What was odd for a quintessentially "gun guy" film and book series, there was a lot of goofs. And I don't mean just the wacky ones like a gigantic .44 Magnum revolver with an equally huge silencer hanging off it. Naturally, there are others, often in the horror genre, that I read from time to time.
But I've meandered enough. Do the goofs ruin the book for you? Or, nah, no biggie? What were some authors and genres you found surprising to find such therein?