Hi Mike, it depends on the finish of the bore. When you "break in" a barrel, you are essentially lapping it with projectiles then cleaning it and polishing it with fine abrasives to remove microscopic burrs to finish the polish.
If you purchased the highest grade barrel offered by the manufacturer, it means that more care was taken to polish the bore before you bought it. In most cases, nothing needs to be done at your end apart from your normal cleaning routine and copper fouling removal as it builds. With lower grade barrels, the bore is rougher and may require a break in using not only copper fouling remover but also an abrasive paste after a given number of shots.
I test and accurize factory rifles on a weekly basis and to be honest, it is quite easy to tell which ones need to be "broken in". I will give you an example of a good bore followed by the worst case scenario.
I purchased an ultra match grade barrel a while back and after the rifle was set up and test loads ready, I went to the range. I fired off something like 12 loads (4 batches of 3 loads), then swabbed the barrel to remove the powder so that I could inspect the muzzle. Looking into the muzzle, there was barely a hint of copper which told me that the bore was giving optimum performance. Furthermore, the rifle grouped in a consistant manner with no big fliers. No need for a break in.
On the latest batch of Howa rifles, the bores have been very rough. This batch has a Hogue stock and is marked Illinois on the barrel. After bedding etc, the rifles need 1-2 fouling shots, then I will get a .250-.3" group, the next group will be around .75", the next group around 1.5". After swabbing the barrel with Hoppes, it is apparent that the fouling is heavy. On inspection of the muzzle, you can see the button chatter marks from manufacturing and the heavy, bright orange copper fouling. These bores have needed a long and harsh break in period and won't come right until a couple of hundred shots have been put through them along with plenty of abrasive hand polishing with Autosol on a jag/rag. (the Howa/WBY Vanguard rifles prior to this were immaculate and did not suffer such problems)
Stainless is not really a heck of a lot different to chrome moly. Both are high carbon, high Chromium steels and both require similar finishing systems. I have a stainless polishing division of our business so this is pretty much up my alley. We also polish many other types of steel inclduding chrome moly. Just remember- each barrel has to be taken on its own merit due to batch variations of the steel and human error during machining and heat treatment. Human error is common and not a problem in itself- nobody is perfect. It only becomes a problem if you are dealing with people who will not concede that mistakes will be made from time to time within the workplace. When that happens, you have no comeback if something really is wrong with the barrel.
Apart from that, its up to how much the consumer can afford with regard to the internal polishing of the barrel as previously mentioned. The less you pay, the more likely it is that you will need to break that sucker in over a long period of time.
Hope that helps.
