Re: chamber chroming
first of all, to chrome plate the chamber is going to be a bear to get right. Yet it can be done. You simply can't put three thousandths all the way around on the barrel. The chrome won't stay put (probably won't if done right as well). You need a minimum of a .008" coating after it's finished out, and .012" would be a lot better. The idea of doing it will end up being very labor intensive. You simply can't just plate a small part of that chamber on a whim. It will involve cutting the chamber about fifteen to twenty five thousandths oversize (all the way around). Then you must mask it off (they'll have a lot of not so nice words for you by the way), and copper plate the areas to be chromed. Then you go back in there and re mask the chamber area again, and strip the remaining copper. Now you are ready chrome plate the chamber.
Ok now you got this plated up barrel, so how do you fix it? Forget using a reamer or a lathe. Stuff is too hard. You'll need to grind that chamber, and now the cost rises like the Apollo Moon Rocket! Plus I'm not sure they would ever get the shoulder to case body area right. But to further mull up this grand scheme, the chrome won't stay put in the chamber. The heating and cooling from shooting will assure this issue alone.
There is a really nice spray metal process that actually is machinable . Also expensive. I've used this process in the past, but it's also not recommended! The other way is electroless nickel. There are two kinds, and one plates within fifty millionths, but the chamber is bad.
I'd simply forget repairing the barrel! Also are you sure the chamber is actually in the form you say? In an auto, the chambers are often cut differently than a bolt gun. They're usually oversized and tapered to aid feeding. I'd send the rifle back to Remington, and let them fix it. I can't see how anykind of a brush could do that much damage (maybe stainless steel). If the rifle shoots OK, I'd just live with it (most I've seen shoot 1.5" groups or worse)