I found a small chip in my upper tonight while cleaning. Not sure if it's new or not. I've fired at least 2000 rounds in this upper, haven't kept count.
How much do I need to worry? Has anyone seen this happen before?
I wouldn't worry about that not one little bit. If it was a crack then I would watch it but I would still shoot it. The bolt just slides back and forth in there so there is no real danger even if it did break through. That little dent chip what ever it is is nothing to worry over unless it gets 100 times worse.