Powder could be the culprit as well. I was playing with one of my 6.5-284s and testing with Reloader 17 and groups at 100 were outstanding I'm talking in the .2s-.3s for five shots. I shot in a 300 meter match with this load and could barely hold minute and a half groups. I was really stunned to see such poor grouping in relatively good conditions so I set up a box at 100 to shoot a nice tight clover leaf. Shot again at 300 meters and again poor grouping. I have since gone back to my H4831 Load that holds half MOA or a little less and holds it out to as far as I can shoot with it. Only thing different between the two loads is the powder. Same cases, same bullet, same primer and same jump off the lands everything. I still cant explain it.