Did that used to say burst or auto? 
For the money you spent, send it back. It shouldnât matter if it just works. You paid for a quality tool, and that is far from quality work. You bought a new gun, it should look like a new gun. Hold colt accountable for their work. Buy a new car with a big scratch, you talk to the dealer and have them make it right. Buy a new pair of shoes that have a cut in them, you would take them back and get a replacement. Its unacceptable, if they arnt held accountable. Things like this will become common place. This is of course assuming you bought it new. OtherwiseâŚ
Leave it alone.
Any type of refinishing will ruin the value of your gun.
I have a number of Colt receivers that have those grinding marks on them.
If you keep buying Colts, you will see more of this and it will drive you crazy if you worry about it. Just let it go.
That is not from machining.
Those marks are from grinding.
Question is, before or after anodizing?
Was the previous owner a bubba gunsmith?
Itâs been covered many many times before, but unfortunately itâs next to impossible for everyone to get the memo.
If youâre looking for a Colt with a perfect finish you have to inspect and purchase the rifle in person. Ensuring that the Rifles have a perfect complexion is the last thing Colt is concerned about. Iâve owned many and most have had love marks.
If it bothers you that much then dump the Rifle and find a new one that meets what your looking for or refinish it. I personally wouldnât worry about it. Itâs a well made weapon and thatâs what really counts.
The problem here is, most of you assume itâs just a cosmetic blemish. If so, no big deal- blend it out, treat & paint. However, it could be something deeper. Granted itâs hard to tell from the photos, but how do you know itâs not a deeper imperfection? How do you know itâs not inter-granular? How do you know itâs not a hot or cold spot? Do you know how deep it runs?
Cosmetic or not, it larger and deeper than usual and the material is also smeared. Look at the edge of the oval. Itâs smeared. It does bear further investigation (note that I said âinvestigationâ not âdramaâ).
I know many of you guys are hard charging bad-asses but you gotta pay attention to the technical details as well. Quite a few folks here are good at breaking things but sometimes I wonder how many understand how to build something. Youâll growl how a lesser carbine will break just as a horde of smelly bearded guys come pouring over the hill, but you wonât take time to make sure an imperfection wonât do the same because âOnly sissies worry about cosmetics!â
The gun was bought new and as shown last Sept. from a local retail for $1,050. I donât know whether that price was supposed to reflect the defect or not, but the salesman did not point it out. Academic at this stage though.
This is also my first AR by Colt â Interesting that a couple of folks specifically indicated this kind of defect is typical for Colt.
Thanks for the many perspectives and options, which I will consider carefully.
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False. Give me at least 30,000 so I can properly burn out a barrel. 
I had a Colt H-Bar with damage which looked similar to that pictured by the OP. I purchased it as a cosmetic second at the time and I saved a decent amount of change but after a few years and reading some misinformed guidance over at another AR15 based forum stating other posters had seen cracks form from the damaged area I contacted Colt who sent a call tag for the full rifle to be returned for inspection.
After about three weeks Colt returned the rifle stating they function tested the rifle, replaced the BCG and barrel and replaced the pistol grip which had a small chip in the bottom corner. Nothing was said about the finish imperfection or done to correct it.
So basically Colt considered it a none issue and replaced three parts I didnât claim to have any issue with.
Strange stuff for sure but the rifle shot better groups afterwords with the new barrel so it was still a win for me.
Time to bust out the Bondo! It does look like Colt used a .mil lower and ground off the marking for the missing fire mode and it probably wonât hurt the functionality of the gun, but I agree with Mistwolf - that level of damage warrants further inspection. I can imagine all kinds of stress fractures forming over time.
I wouldnât say that is the âNormâ for Colt. However, I do agree with a few posters here (sottryan is defintely spot on) that Colt isnât known for âgood looksâ.
All but one of my rifles are Colt 6920s. Every one of them has had some type of âBlemishâ in regards to finish. Iâve only had 1 colt that had to be sent back because of a machining glich. That was (IMHO) a fluke occurance.
One thing I do agree with is what Poly saidâŚwas that grinding done before or after anodizing?
Contact Colt. Let them know your issue. They may ask you to send it in or they may say it isnât and issue. One thing I do know, if there is an issue with machining they go through the issue and fix it.
I got a pretty cool âover the phoneâ class on what they did in regards to my lower. Their tech guys are straight and to the point with no BS, at least from my experience with them.
I believe this is the number youâll need.
1 (800) 962-2658
I have the utmost respect for Colt and have owned at least one Colt firearm since I was seven (all 1911s), but I would never buy a Colt AR. They seem overpriced for what they are. I guess thatâs why the phrase âpaying for the ponyâ is so well known. I donât ever plan on selling my ARs so the resale value argument is a moot point. Anyway, I hope they take care of you.
Huh? Colt ARs run the same price as most other guns if you look around. They were overpriced in the panic, but they pop up in WallyMart for their regular $1100 or so price again now according to posts Iâve seen. 
1st the marks donât look deep enough to have ground off any marking and a similar mark would be present on the other side⌠2nd the selector says fire when it would say semi rather than fire on a mil lower⌠3rd the internal milling of the SF lower should be different than that of a semi to accommodate the SF FCG.
I would send pictures to Colt⌠they will tell you whether it needs to be returned or not. I like it though⌠gives the rifle character. Colt makes a shit ton of rifles and as long as it wonât cause any functional issues later on, it is a nice distinguishing mark.
Well, overpriced as in for the features you get - no CHF barrel, at least a few dings in the finish, and base M4 furniture. Iâm just sayin - you could build an equivalent rifle for less IMO.
Good point⌠I didnât think about the Semi thing⌠Hmmmm⌠Gotta scratch my head on this oneâŚ
I usually piece guns together⌠and donât own a complete factory Colt for the record⌠But for the price of a BCG alone, beating a Complete Colt is tough.
True⌠I wouldnât mind owning a few Colt BCGsâŚ
That makes the $1,050 I paid at a relative up-scale retailer sound not-so-bad. (Maybe that price included a booger factor.)
Sounds like the concensus is to send it in to Colt â Iâll have to weight whether itâs worth the hassle.
Iâm steering away from attempting a refinish though. Either (1) petition the maker, (2) leave it and lump it, or (3) sell.
I do not know if I would buy an AR right now without holding it and checking it, no matter the make. Over the past 6 months all the companies have been rushing them out their doors as fast as possible. If there ever was a time to see some problems, not just in finnishâŚbut in overall quality control it would be in guns that have been hitting the shelves over the past couple of months or so. When humans get in a hurry, they make mistakes.
This blemish is 3D. Call Colt and talk to somebodyâif you send it back, make it to this personâs attention if possible. If uncorrected and you try to sell it later, nobody will believe this is factory.