If that was on the inside, I'd be concerned. Since its the outside its cosmetic. Should it have been blem-ed, possibly. But in all reality, that happens much more often then you think on forgings. There's a mark like that on the bottom of my ACOG, doesn't even phase me.
If you wanted a mil-spec, get it done rifle thats reliable, you got it.
If you wanted a pretty safe queen, well, go billet and don't fire it, don't breathe on it.
Make that your beater gun and run it, after 1200 rounds, your going to freak when your brass deflector shows aluminum and the hard-coat is gone.
Here's a list of things that we all want pretty, but in reality, are unobtainable.
-Race and Track cars
-Firearms that are actually used (like, do you run it weekly/bi weekly, or only 6 times a year)
-Girls of the night
There's more, but that's probably the first top three that come to mind in 5 minutes