Hard chroming the barrel was made very popular with service rifles during the Vietnam era due to the high moisture and the lack of cleaning that was gievn to some weapons. Many AR-15 manufacturers still offer this, but it was found that quality steel and stainless steel barrels had a slight accuracy advantage due to several reasons. First, hard chrome is...well....it's hard....but it is very thin and doesn't polish easily. Chrome generally takes on the characteristic of the metal it is applied to. In other words if you hard chrome a matte gun it will be hard chromed and matte. If the gun is polished, the HC will look polished. Barrels become more accurate after firing break in rounds due to being polished. HC goes against this to some degree. Another fault is that after a bunch of rounds are put through the bore, the HC can chip, particularly in the chamber. Having an irregularity in the bore or chamber is a place where copper fouling WILL occur and degrade accuracy. Having a barrel flake at the crown would hurt a lot as well.
Some people do still prefer the treatment for a SHTF scenario, but if you are intent on max accuracy, then hard chroming the bore is not the best route.