Having a borescope really helps to determine just what you're starting with in terms of any break in to do. The better the barrel quality, the less there is to do - if anything.
This is the technique I've been using for 25 years - and I'm still really just guessing, based on past successes, so take this for what it's worth.
Using the 10X Hawkeye borescope, I look over the entire barrel, with particular attention paid to the throat, gas port, and crown. Chamber concentricity can't be measured this way, but you can see if something is not right. This once kept me from accepting twenty SS barrels from an esteemed barrel maker I will no longer use.
There's a surprising amount of crap (release agent?) left inside a new chrome lined barrel, typically. I'm talking top shelf like DD and Noveske. I think chrome lined barrels benefit from a good scrubbing with JB Bore Paste or KG-2 prior to shooting. Chrome is harder than woodpecker lips, but this does I think help smooth things out you can't even see at 10X. It at a minimum gets all that nasty copper colored stuff out. The barrels treated this way seem to stay cleaner longer, too.
VFG felt pellets (from Brownell's) with KG-2 will help smooth out any tool marks left in the throat or at the gas port with any barrel. Stay away from the crown, meaning if you push the felt pellets (I use two at a time) all the way through, you remove the tip and start over at the throat. I'll use a hundred 2" strokes in the throat, tightening the felt pellets on the cleaning rod every twenty. Then twenty passes on the entire bore.
I just use high quality SS barrels from Craddock Precision, Proof Research, and V Seven, so there's really nothing left to do with these barrels in terms of break in.
A couple of minutes with KG-2 in a new throat won't hurt, though. It's far less expensive than the ammo used in a typical break in, and dumps zero heat into the barrel at its most vulnerable point.
