- Mar 6, 2008
This is a thread for discussion of the article, The Over-Rated Crown, By Alan Marshall. Here you can ask questions or make comments about the article.You probably think having a perfect crown is important to accuracy. I think so too … although this article will make you wonder.
Background: I was told that one of the major chronograph manufacturers checked the velocities of the rifles of three officers so they could determine their come-ups for various ranges. The rifles were described as being similar, as was the ammo. What was interesting was that the bullet's Ballistic Coefficient (BC) when fired from Rifle 1 was different than the bullet's BC from Rifle 2 and from Rifle 3. In fact, each rifle could be distinguished by the BC it produced. (As an aside - Was the rifle with the highest BC also the most accurate?) So the question is - What caused the difference? It wasn't the ammo, since the same ammo was used in all three rifles, and it wasn't the shooter. It must have been the rifle, but what part of the rifle? My first thought was that maybe the crowns were a little different, perhaps by cleaning rod wear or a less than perfect crown to begin with. It made sense to me that a perfect crown would allow the bullet to start its flight with very little yaw, resulting in the highest BC possible for that particular bullet. On the other hand, a crown that is off center or has a ding in it would allow gas to exit non-uniformly and thus kick the base of the bullet a little to one side as it left the muzzle, resulting in a wobbling bullet with greater drag and a lower BC.