After having tested several hunting rifle barrels from new, my observation is that, in general, rifles improve in accuracy to some degree if not broken in at the factory already. But all new rifle barrels should be cleaned before you put bullets through them whether broken in or not. I find residue in all cases for new barrels.
On new rifles and barrels I use a solvent laden bronze bore brush and then 1 soaked patch of your favorite bore cleaner that also addresses copper fouling and then around two or three dry patches. Web research on chrome lined barrels is that you should clean it like an unlined barrel just less frequently some say after 200 rounds. I bore snake my AR barrel after each outing as a practice but did not use any specific method to break it in, believing that I did not need a regimented plan. After a session of 20 or 30 rounds I have touched my chrome lined barrel for heat and find it just warm to the touch and never hot. My AR is new and has only 150 rounds through it. Some say the barrel is not broken in yet. I would strongly avoid any abrasives in a chrome lined barrel as it will surely wear the chrome away. And be very reserved in its use for break-in on steel barrels. I scrubbed the barrel only once with a brush since new and wont scrub for another 100 or so rounds unless groups deteriorate.
On hunting rifles I have use JB Bore Bright, (an abrasive) very sparingly if groups seem out of normal but in general it does not get used much at all.
I once tested a 300 Ruger RCM that shot 1 3/4 groups at 100 yards but later tightened after use and normal cleaning to sub-MOA. The truth is just the shooting alone may have cleaned the bore or as some say, shooting seasoned the barrel.
I think it is a best practice to at least run a bore cleaner soaked swab through a bore if your not sure of fouling. How the swap comes out is the tell all.
I avoid using soft copper bullets in my hunting rifles as cleaning can be a pain to get soft copper out of the lands and grooves. Some folks swear by them, I swear at them.
I prefer the harder gilding copper which is used on regular hunting bullets and on some brands of solid gilding copper bullets such as the Nosler eTip® that I just used on a whitetail buck this past fall. Don’t over do barrel cleaning and remember to take some fouling shots before shooting for group. At least one and perhaps 2 or 3 is better.
A hunting story of barrel cleaning and lack of it comes to light as a hunting friend of my father shot a Savage 300 in the deer woods. He shot that rifle one or two shots before the deer season then hunted with it. Never cleaned the barrel after many years and when others complained that he never cleaned his rifle the would put a hole in a coke can at 50 yards to shut them up. I am not sayin’ never but his rifle never had “solvent stink” and oil smell in the deer woods and he killed lots of deer.
On the target range is another story, there you don’t care about smell you want clean!