Chrome lined 20" barrels are still several weeks out (4-6 at last update before they arrive in house, then another 1-2 weeks to go to the coater's). Chrome moly steel is where chrome is mixed in with the steel at the metalurgy stage. This makes it a bit more durable and corrosion resistant. Chrome lining is where the bore is oversized, chrome is shot down it, then the bore is recut. The chrome layer that is left is very slick and durable. The down side is that the layer of chrome is not uniform, meaning that there are some parts of the barrel that have a thicker or thinner coating than others. This is why chrome lining is not as accurate as chrome moly or stainless.
Hopefully this helped explain a few things.