1st groups today were tight with my 6x284,after 20 rnds last group of the day ( Same load) were greatly expanded. If I was shooting a 308 I'd still be getting tight groups well after 20 rnds. Both cartridges bbls collect copper. Why is the one more sensitive then the other ? On Military Channel there was a story of a sniper making critical long range hits all day long with his sniper rifle. He didn't stop to clean it ? My 6x284 has a Cut rifled Brux bbl ?