My experience indicates more problems with cases necked up, rather than down. For instance, necking 22-250 cases up to 250-300 AI. A "doughnut' will develope at the neck shoulder junction. I found this on my 2nd firing of the cases..sized cases chambered fine, but when I seated a bullet, the doughnut was pushed out, making for hard chambering. My normal sequence when loading is to try both empty sized brass in the guns chamber, then the first charged and seated case. So I only had one loaded. I ended up outside neck reaming. Getting a little smarter, I found I could discover the doughnut by fitting a bullet into the fired case. The bullet would stop at it in the neck. Those fired cases I inside neck reamed.
I now use plentiful 6.5 Creed cases, neck down..no problems.
