You are checking material type and hardness?

I don't think you will be happy with any answer I give, but I will not buy a bolt unless it is made from C158 material if that answers your material question.  If I remember right almost all of the C158 bolts come from one of a couple places unlike many of the 9310 bolts being made by smaller manufacturers.  The carriers I don't really care that much about as long as they are M16 profile 8620 and have a staked gas key.  By doing my own inspection I am talking about for obvious defects such as this bolt by the OP that should have never left Colts factory.  All the bolts I get are usually MPI/HP tested as well which should show any defects the same as a Colt would.  Everyone makes mistakes, and I figure overall Colt has a lower percentage of bolts that get past QC inspections that are bad then someone like PSA or ToolCraft.  But I doubt the percentages are that far off, maybe not even any.

There really doesn't seem to be that much difference in any of the well known BCGs as long as they are made out of milspec C158 bolts - I know many will disagree with me on this and it is your right to do so.  I don't blame anyone for wanting to get a well known high quality bolt from Colt or BCM or FN, but I really don't think PSA or ToolCraft will fail any earlier then the more expensive ones for half the price.  If I had to pick one out of any of them I would choose the BCM just because they seem to go the extra mile for QC inspections and it is more likely if you ordered 10,000 BCGs from them that you would probably not have any issues like this whereas one of the others you might have 1 bad one - but I doubt it. For a lot of people like myself, we are happy to get a BCG for $80 instead of $170 that 99.9999% of the time will be just as good as the more expensive one right out of the box.  And if not you will generally be able to tell rather quickly.  Check out the 100,000 round + M4 thread where all the PSA bolts are holding up just as long as the higher priced bolts.  Please don't take this post as me bashing Colt, as that is not the case.  I love Colt products and would be happy if all of my rifles were Colts, but I like to shop around and know if the extra money is really worth spending on a product and in this case I just don't see it being worth it.  Maybe if the price difference was $20-30 instead of over twice as much as the cheaper ones.

Have you been firing the rifle yet?  The bolt markings are so fine, carbon easily obscures them.  Clean the bolt and I bet the marking show up.  When I checked mine for this thread, I had to clean one of them before I could see the markings.

Just squeeze another gas ring in there. Looks like that would solve the problem of them moving around.

I'm still waiting on shipping information. I will send it in and get it replaced with a bolt that's in spec if I can.

If it passed QA/QC, whoever installed the gas rings should have noticed it. Of course, the person installing the gas rings could have no knowledge about what the bolt should or shouldn't be profiled like.

The distance between the ridges is correct at the bottom of the groove so that the rings are in the correct position when compressed. There is just less support at the outer part of the rings.

Is it possible the rings weren't installed by a person but a machine?  If it was a person doing it I don't know that you could claim ignorance to the bolt design since he/she would obviously see 1000s of them a day.  Just like if I was to work on a bike pedal that I have no knowledge or interest in - if I seen 1000 or more of them a day I am sure I would notice if something wasn't right.  

Glad to hear they are taking care of you though.  In a way I am a little surprised they took it back so easily.  If you were the original owner that is one thing, but buying it from another individual I figured there would at least be a couple questions involved with who you got it from and his purchase etc.  I figure this is a fairly rare occurrence for them though and it is always best to make the customer happy if it is your mistake because you never know who may be watching the results - such as 1000s of fellow members here.

What did Colt say?

Colt has the BCG, no word yet.

I got a replacement bolt today. This one doesn't have the large radii that the original had. All they said was that there was excessive play in the bolt rings.

No. Stamping is a process. Dot matrix is a pattern. You can have a stamped dot matrix.