Back in the 60's when Remington came out with the 7mm Mag, the barrels were blued stainless. I think they iron plated them so they would take the bluing. That was before the time when folks wanted to take bright shiney metal in the game fields. Now, it is somewhat the rage, so they can eliminate the step of treating the stainless to take bluing. Other non-glare surface treatments have been developed and are available now too. Times change - sometimes good, sometimes not.
EJ