I have a WInchester model 70 Super grade in 300 WM thats been a safe queen since I bought it new in 2011. Ive recently started hunting with it since I have access now to some rather large been fields. So naturally Ive started shooting it more and what I have noticed is after about 10-15 shots the groups really open up. When I clean the barrel you can tell its pretty fouled with copper. I bought a cheap bore scope and its easy see Its fouled. The rifle really likes 200 grain partions with 70 grains of 4831 SC. Just curious if some calibers foul more than others or if anyone else has noticed this also.