I know this is an old post but figured I'd share what I know.
First, those are very reloadable. The next time you fire them the dents will pop out and reform the casing inside the chamber. I would not be concerned as those dents are fairly minor.
Second, if you don't fix your rifle they will get dented again. The AR I built was doing this. I have a BMC MPI M16 BCG. The ejector spring (not the extractor spring) was way too stiff. I ordered a 3 pack of ejector springs from Brownell's and trimmed one using this info
http://www.gswagner.com/arejector/arejector.htmlI did the first one exactly as the website said to do. I was getting 1 or 2 casings stuck in the ejector port out of every 30 round mag but the case denting was gone. I shortened another spring, this time not as much. My original cut took about 4 loops of the spring off. On this spring I removed just 2 loops. The result is about 800 rounds fired with no hang-ups in the ejection port and no more denting.