It’s always good to clean your gun and keep it in top-notch shape. Why, then, would you intentionally foul the bore by sending a shot down the barrel prior to heading out on a hunt?
Distinguishing fact from fiction is as challenging in the world of firearms as it is everywhere else. Here's one perspective on firearm cleanliness, from author Tom Tabor in his Gun Digest 2013 article, “Ten Shooting Myths Exposed”:
“How could anyone make an argument against firearm cleanliness? Well, I can think of only a single instance when a little dirt might be a good thing, and that is inside your gun barrel when it comes to heading out for a hunt. One of the factors necessary for consistent shot placement has to do with the consistency of the firearm bore. Simply put, a round fired through a clean bore will almost always impact at a different point that those shots that follow—and that first shot is often the most important you will take in a hunting situation. I have frequently found the amount of variation can be from about an inch all the way up to three or four inches at 100 yards. If you never shoot past 50 yards, this might not be an issue of concern, but, if you find yourself trying to pull off a shot at a recordbook bighorn ram on that once-in-a-lifetime hunt at 400 or 500 yards, it could easily become a substantial problem to overcome. I like to remove all the variables I can and, in so doing, I always send a round down the barrel and foul the bore before heading out to hunt.”