I saw a good topic on cold barrell shoot last night on ch406 . a clean cold bore will throw a bullet off a ton at longer distances , so remember when hunting a slightly foulled barrel is a good idea . For me it will be a 6.5x284 with a break I want to see impact through the scope . 140 vld !
Why? (I have never noticed this problem)
Then you've lived a sheltered firearms life. 
Not sheltered, maybe it has to do with how I clean it. I asked why, because I was wondering if it had to do with some people leaving oil in the barrel instead of running patches until it was completely dry.