That's really the issue. Many of these factory barrels shoot really well, even with all the machine marks left in the barrel. If you look in there you would be shocked that a barrel that rough could shoot well. But, they do.

My Axis is pretty accurate, good enough for .5moa on a regular basis. But, if I clean all the copper out it shoots poorly until I put 10 or 20 rounds through it.

The bottom line is if it shoots good enough for you then leave it alone.