This report is going to start a controversy, because it dares to question the things that are currently held dear among airgunners and firearms shooters, alike. Sorry, but here it goes.
What is a crown?
The crown is the end of the barrel, or the place at the muzzle that has the final influence upon the bullet as it transitions to ballistic flight. One popular belief is that if the crown is not perfectly symmetrical, then one side of the pellet or bullet can exit before the other and allow escaping gas to impart a destabilizing effect on the bullet at the beginning of its path to the target. So, crowns have to be perfect, according to the vast majority of shooters.