I think Fred is correct, neck turning helps. With that said I do not turn necks unless I have to. I have made 221 fire ball cases out of 223 brass, you better turn the necks or you are going to get a lot of pressure build up because the necks are too thick. I have also made 222 cases out of 223 and 30-30 out of Win 375 cases and they do not need turned in most cases. Neck turning does make a gun more accurate, but not by a whole lot. If you are getting 1" groups you are not going to drop it down to .5 by neck turning. Maybe a couple of tenths., maybe. I am not trying to get to the top of the bench rest world, just hit a varmint when I have notion to. Just my 2 cents