I recently purchased this new Colt M4 just this past February and I have taken it out to the range every weekend since.
On average I will shoot a hundred rounds through it every weekend.
This past weekend while I was giving it my normal cleaning I noticed that the bolt carrier seems to have a nick in the rail that can probably be better described as a metal shaving or Burr.
While in the images provided below it does not appear to be extremely large it is large enough to scrape your finger as you run it across the edge the edge that mates up to the upper receiver.
In my 30+ years of owning ARs this is the first time I’ve ever had a BCG show signs of nicking or burring on a fairly new bolt carrier.
Has anyone else experienced this and should I be concerned or should I just try to file the burr down to a smooth edge?
I’ve seen that before (my current BCG’s may all have it for all I know).
I’m not an expert but I believe it comes from the machine that cuts the bolt carrier either “chattering” briefly on the part or a piece breaking away from the bar during machining.
AFAIK it’s nothing to worry about and won’t get any worse.
That’s nothing to sweat at all. Could have been done during machining, but nothing to worry about. The only thing I’d make sure of… is that no burrs stick out on the bearing surface there. It doesn’t appear to be the case from the pics.
Is it common to inspect ones weapon so thoroughly?
It’s cool to sniff around in there. I like to study how stuff interacts and wears. Now if this gets to the point where he’s calling Colt, then we’re going to have problems. :sarcastic:
I HAVE TO SAY ‘YES’.
Over the years I’ve felt like an unpaid QC inspector. The basic things that firearms manufacturers sometimes forget to do almost makes me want test reports on even the parts and their metallurgy!
Remember the Colt carbines sold through Wal-Mart that came with unstaked bolt carrier keys?
I rest my case, Your Honor. 
If there’s a burr that might bite into the upper receiver bearing surfaces, just take some very fine sandpaper and polish it smooth. I do this with all of my BCG’s anyways… almost makes the action as smooth as Megan Fox’s butt appears to be.
I can picture that. Nice thought, thx. 
These are normal machine marks.