Mod 12 with aftermarket prefit barrel. Using Varget 30.2gr, 105 hybrid's at 2900fps. Worked out to 1000 yards on steel targets. Barrel was never abused. Max 4-5 shots before a cool down, commonly with a chamber chiller. Standard results were cloverleaf at worst at 100 yards. Suddenly went to 2MOA. Teslong borescope shows firecracking, and burring at the beginning of the leade. I've never used an abrasive in the throat of a barrel. Assuming I try using an abrasive to clean up the throat, how many more shots can I realistically expect from this barrel? Numbers I've seen lead me to believe that 1200 rounds is low by 700-800 shots. But, it is what it is. I've got a Shilen from Jim that's been sitting around for a while, ready to be installed. Based on experiences, should I just put the Shilen on, and forego the abrasives?