Copper fouling can and will effect accuracy. Extreme copper fouling can ruin a barrel. This is way it is reccomended to "break in" a new barrel.
Picture this. Every time a bullet (copper clad or solid) is fired, a minute amount of copper is left behind. Each shot afterwards leaves more copper. At some point, the copper build up becomes excessive and instead of leaving copper behind, it is now removing copper,,,,, and a microscopic piece of the lands(rifling) go with it. To many pieces of the lands being removed is whats refered to as a "shot out" barrel. Constantly firing shots from a HOT copper fouled barrel is sending it to an early grave.
I have taken many guns that people say will not shoot well anymore and copper stripped them. Accuracy returned if the barrel has not already been shot out.
The purpose of breaking in a new barrel is to "slowly" smooth the bore in an effort to minimize copper fouling. Lapping the bore is one method of breaking in. Fire lapping is another. The end results is to have a barrel that will allow more shots to be fired before it copper fouls.
There is a product called WipeOut that will remove even the worst copper fouling with little to no effort. Its like a shaving cream that is injected into the barrel and left for an hour or so to do its thing. Extreme fouling may require 2 treatments.
IMO, This is the best copper remover on the market.
HTH