I have a 260 remington with a criterion light varmint barrel/ 1-8 twist.This barrel replaced a factory barrel. Gun has a accustock and accutriger. Had this thing shooting extremely well. Groups all of a sudden really opened up. Did nothing to the gun. Probally had about 350 rounds thru it when this happened. Cleaned it more than once and can't seem to find a load that it will shoot nearly as good as before. Was shooting 0.350 groups at 100 yards with accubond 130 and 140 grain bullets. Having a hard time finding the inch mark right now. Ideas???