Unless you are using coated bullets like the Barnes xlc,some fouling will be deposited on the barrel whether you shoot a 30-06,or a 30-378.The standard Hoppes #9 will not remove all of this fouling,and as a result this fouling will build up,and over time this copper will start to effect accuracy.I have heard several people complain that their barrels were shot out because the accuracy was falling off ,despite regular cleanings with a regular powder solvent like Hoppes #9.However,once sweets or cr-10 was used in these guns(in some cases,it took hours of repeated applications because the fouling was so bad),the accuracy miraculously improved.According to them ,these people didn't have problems with copper fouling either.The use of sweets or cr-10 on a regular basis will remove this copper and prevent it from accumulating and leading to problems later on.It's a lot easier to prevent a build up of fouling by using a little sweets each time you clean the barrel,than to let it build up then spend a great deal of time and effort trying to remove it later.