lwpdx ,
Barrel crowns have a significant affect on the stability of the projectile as it exits the barrel. A good single hole group for an airgun at 50 yards, is what is expected from a precision rifle at 200-400 yards. For precision rifles, the crown can make the difference between a sub1" group, and a 4inch group. Every once in a while there will be an exception to the rule, but for the most part a proper crown at 11°-12° will be the most accurate. The effect of The effect the crown has on accuracy is usually more pronounced the faster the projectile is traveling, which may be the reason crowns are not as important on airguns. (I'm a powder burner guy before an airgun guy, so the exact science of subsonic ballistic stability is a bit beyond my knowledge)