It's never too late to break-in a barrel and a lot of guys dont do it at all. IMO, it's best to do it right away, but the bottom line is, if you get the bore cleaned down to bare metal, it shouldn't be much or any different than new out of the box. And in fact, most rifles have a few shots through them before they are boxed.
Important thing for break-in, get ALL the copper and most of the powder out of your bore. Most guys "think" they are getting all the copper out when they get a "white" patch, but that's seldom the case. Two good products to use at the range are Bore Tech Eliminator and KG12. I have used Bore Tech but not KG12 but I hear that it's better than BTE. I wet patch through with BTE until I start getting light blue patches. Then I scrub a little with a nylon brush and let it soak for about 15-20 min. The ptach will turn dark blue again. I repeat this process until I'm not getting any blue. At that point your bore should be about 99% free of copper and about 80-90% free of carbon. A little carbon left in the bore is not a bad thing, at least not according to Dan Lilja. I use a nylon brush because a bronze brush will be eatened by a good copper solvent and show a false blue on your patch.
Breaking-in a barrel is about conditioning your barrel so it fouls less... not about accuracy. Accuracy may or may not improve, but you probably wont notice much difference. The benefits of break-in are easier cleaning and longer shooting strings before you need to clean and maybe less fouling shots needed after cleaning to "settle" down your barrel. That's it.
Cheers and good shooting,
Mark