Graphite? My recent lot of 147gr HST seems to do the same thing.
I've noticed similar things on other ammo... usually cheaper ball. Wolf 9mm (ages ago, when it was lacquer coated cases) was really bad. The USA made Norma 124gr ball I have been shooting lately is a little dirty like this, but also seems to leave tiny brass flecks as well, in the gun and on my hands.
I just wash my hands and drive on.
I don't have such issues with Gold Dot.
I have shot a lot of both and never noticed, but my lots are 5+ years old.
-Seconds Count. Misses Don't-
I did the same thing, finally got to the end of the Gold Dots and have been accumulating HST for a hot minute. While I did not specifically notice that last week at the range, I’m not surprised.