I'm not suprised. Most magnum chambers are a bit sloppy. When I loaded magnums, I always got that expansion ring in front of the belt before I ever had to resize. I think that had I partial resized back then, I could have increased the case life but would have had to trim now and again. By partial resizing you change the relationship of the shoulder of the case to the chamber. That reduces streach in the belt area when it's fired increacing case life. I have to admit that in my magnums, being conservative was not in me. My favorite load in an old L61R Sako was with the 160gr Speer and a charge of old N205 that was 4grs over max. I'd had it long throated prior to developing that load.