Not a myth. You want to know where your first, cold bore shot will hit. Instructor at a long range rifle course I took really reamed me out for cleaning my barrel first evening. Said my cold zero would be worthless. Didn't clean the gun for the rest of the course(500 plus rounds). Instructor had a custom .308 on a Remington action, I think he said a Rock barrel (don't recall exactly) that hadn't had the barrel cleaned in over 3000 shots ... and the groups were getting better.

Practically speaking, though, for those of us who don't shoot hundreds of rounds a week, okay to clean your barrel and hunt with a clean bore. Just be aware that your first shot will not impact at the same point as your groups from a warm, dirty bore. The "cold zero" on my .308 is .75 inches left and .5 inches low from normal group center. As long as I know this, no problem. And how do you know? You need to record where your first round hits every time you shoot.

I'm not picky on bore cleaners. I use Hoppes and Gun Scrubber. Make sure you dry completely and oil lightly if using any of the copper removers that include ammonia.

cogito, ergo armor.