A local guy on a FB gun group was selling a "stag" upper for $275 with BCG/CH.  All I could tell was it was an 20" A2 upper.

I offered him $200 an Anderson stripped lower and $30 in ammo and he took the deal.  

I got the upper home and noticed it was marked "CM" in front of the rear sight the M is slighter of set lower than the C.  There are also two marks on the front right of the upper one is a triangle and under that is a three sided box with a c in it both are faint.  There are no F marks on the FSB.  The hand guard has single heat shields.  The barrel is marked C MP 5.56 NATO, on the MP the long part of the P is the right leg of the M.  The front take down hole looks like it has a spacer pressed in to make it small hole.  When mounted on a lower there is a noticeable gap between upper and lower.  The bolt would not go into battery and was filthy, I tried it in a BCM upper and it worked fine but the BCM bolt would not work in this upper.  I cleaned and oiled the BCG and upper and found a small piece of a primer in the barrel extension, after removing it the upper functions fine.  The upper has no feed ramps and the extension is rifle.

The charging handle looks like a cheap one and has a lacquer coat, its not parked.  The bolt is marked CMP.  The carrier is full auto and has a C on the left side.  

Do I have a Colt A2 upper and I'd love any ideas of how I should build it?  I think I have an A2 stock somewhere and I know I have a Magpul rifle stock and hand guard, I'm leaning toward an A2 build and would like to make it as authentic as I can without spending a ton of cash.  

I can get some pictures if anyone needs to see a marking.

Thanks

Like a friend of mine would say "It smells like a Colt."  Appears to be a factory assembled large-hole A2 upper with Colt BCG to boot.  So what if the charging handle isn't Colt.  You've got a great foundation to start any A2 rifle build for roughly $280 bucks in cash, cheap lower & ammo.  With the prices of AR parts these days, you could finish your Colt A2 clone for under $500 bucks.  Don't forget to post pics when you're done.  Here's a pic of my Colt M16A2 clone:

 


I'm bothered by the gap between the upper and lower.  I have no experience with the large hole adapters, but it looks to me like thinnest part should be on the bottom to eliminate the gap.  Any suggestions on a good lower to use, I thought about the new Colt stripped ones but they have the built in curved trigger guard.  I'd like something with a low key logo.  

The adapter bushing usually moves around, but some folks will use a dab of Loctite or crazy glue to keep it in place.  I'd use a correct size drift punch and remove it.  Then, you could reinstall the bushing to minimize the gap between upper & lower--it's just something you really can't eliminate.  I used a NoDak Spud gray A2 lower with no logo and the anodizing seems to match my Colt CM forge-marked A2 upper pretty well.