Accuracy of my 338 Win went to pot immediately after I shot 3 3shot groups @ 200 yds that averaged in the 5s. I was pretty pleased. These groups were with new brass. After shooting the brass once I neck sized them which as been my practice with non mag cals. Velocity fell off and so did accuracy. I upped the powder to get back to the velocity that produced the good groups. These loads were just a bit compressed. I could feel the crunch and grind of the powder as the bullet was seated. Had put the orginal loadings on the spinner and things looked pretty fair and thus felt no need to spin further loads. In working with a couple of new powders (4831 and 4831sc) the SC load wasn't compressed at all. The 4831 did the crunch and grind. For some reason I put them on the spinner. The SC uncompressed loads were straigh as an arrow. The dial indicator wobbled like a wind shield wiper on the compressed load. Using standard die set. Haven't shot 'em yet but I can predict the results. Any suggestions? Thanks in advance.