is it 6061 or 7075 just curious.
the grainy texture could be a blown grain, crystalline structure from too much heat during the extrusion preocess, another problem with billet milling.
SAPA used to be one of the worst, now they are one of the best, also known as hydra now.
Rick is probably ignoring you because he doesnt want to deal with as its out of his control, and eating up his precious time. Sell your receiver if it bothers you that much, or paint it and move on, now you know, anodizing is never the same. Oils are added by manufacturers to try and hide or smooth over the appearance.
Also, My $3000 KAC rifle has worse mismatch. From Factory.