Looks like the weighted sample has a 26% black electorate (was 28% in 2010). Interesting that the crosstabs show virtually even support for each candidate across the entire state outside of the inner metro. Also odd to see undecided leaners supporting Nunn 2-to-1.
I'm beginning to think that it's over at this point. At the beginning of the year, you couldn't have convinced me that Carter would have a better chance of being elected. She needs to be up by 4 just to have an even shot of avoiding a run-off. The trend suggests she is down by 3-5, and that's with an inflated count of people voting for Swafford and the remaining undecideds who historically break Republican.
If this poll is undersampling black voters with at least 3%, as you're suggesting, that means that it should be basically regarded as a tie I think. At most we're talking about a Perdue lead of 1-2%, and that's being generous.