Interesting how this old thread popped up. I was going to comment as I read along and discovered I had ALREADY posted!!
Selmer, There is no need to guess if the crown needs dressing. I have a rear eye piece from an old rifle scope. When inverted it is one heck of a magnifier. If you do not have such a piece get a jeweler's loop or a strong magnifying glass. Inspect the crown in bright light and look for a tiny imperfection, nick or an area that is shaped differently. If it isn't uniform around the entire circumference it needs attention.
When a known rifle goes sour I always look at the crown. Many times it is the cause of the larger groups.
