Without fail, a dirty "fouled" rifle will almost always outshoot a clean barrel. I don't clean any of my barrels until accuracy starts to fall off. For hunting rifles I always make a pre-hunt trip to the range to verify my scope's settings and foul the barrel...I then do not clean the barrel until the season is over and the rifle is ready to be stored for the off-season. Most people over-clean their barrels, which will shorten life a much if not more than shooting.