Finally got rid of the copper and carbon...

[Bonas]

to what degree does it affect accuracy?

I'm not sure a hunter would ever notice but I tend to clean every couple seasons but only hunt and slight bit of range time, mentally it bugs me but in a lot of research this barrel cleaning stuff is a bit of magic for sure. Guys chasing tiny groups in competition can see differences we mortals never would and may not ever need to for a hunting rifle, and if using bore brushes you just wear it out sooner. I only use wipe out and patches, seems to work.

As for the lapped barrels, I had a proof carbon, apparently hand lapped and came with an 11 round break-in instruction, shoot 3, clean, shoot 3 clean, shoot 5 clean...done and dang did it ever clean up fast. Pretty amazing. Was left feeling though half the barrel life already gone, my weird mind. It's still a pretty subjective topic, don't get too far lost down the rabbit hole for what your actual needs are. If you can actually see the accuracy drop then that's something and I wonder how many rounds that would take?

I've never noticed an accuracy drop with carbon fouling, but I run a single patch with CLP followed by a dry patch after I shoot, so I don't get much carbon build up. I see accuracy drop off from copper fouling after about 500 rounds in barrels that shoot well. I've yet to notice it in rack grade barrels.