copper sits in these holes or scratches and the copper corrodes and causes further damage and enlargement of the imperfection because of electrollisis and it also traps and holds some of the harsh chemicals that you use to clean the barrel later on.
barrel break in is crucial from the first shot. If you got some rough or tough spots you may need to us some JB bore paste to smooth it up. It is a lot of work and seems like a pain but I guarantee that breaking it in properly will make it a lot easier to clean down the road.
Like some of you I also turned my nose up at barrel break in procedure. But then I got a borescope, and that changes your whole attitude. I know for a fact that I ruined several rifles by ignoring the break in procedure and I lost accuracy in less than 700 rds. And after looking at it with a bore scope I knew why. pits, corrosion it looked like they were stored out side the garage.
Now that I have a borescope I have bought new rifles and I take it with when I am going to buy the rifle. I inspect them before I leave the gun shop. The last one was a Rem 700. The dealer had 3 of them and I wouldn't accept any of them. The barrels out of the factory where that bad. He talked to the rep and got another one in and when I looked at that one it was as smooth as a babys butt. So iI took it and broke it in properly. Now it takes about 10 minutes for patches to come out clean.
If you have time to do it twice, then you have time to do it once right and put your name on it