I understand why parkerized rifles are the norm, but I haven't ever seen an assault/battle rifle offered with some of that old-school deep, rich blueing like on my Colt 1911 National Match. I have seen M1 barrels blued but I think a blued receiver on an AR15 or a FAL would be gorgeous. Has anyone ever seen this? Any reason why it isn't done except for the fact that most receivers are aluminum?