I picked up a NIB Colt 6721 yesterday. I will have to say that the fit and finish (excepting the EPD) is the best I have seen.

I inspected it before I bought it, but I guess not thoroughly enough. The ejection port door will not close by normal means. It seems that the detent is a tad too high, and it catches on the inner ledge of the ejection port, just in front of the detent dimple. The only way I can get it to close is use a small blunt object to depress the detent enough to engage the dimple. I have checked the detent, and it depresses fully under standard pressure, so it doesn't appear to be the detent spring.

The ejection port door will open normally when the bolt/bolt carrier is charged, as it should. I have tried tapping on it with a small rubber mallet, but it will not engage the dimple. I don't know if the detent housing was mounted too high on the port door or not, but comparing to my 2 other Colts it looks the same. I didn't have this problem when I purchased my other Colts and they were new, so I don't think it's a by-product of "new rifle, tight tolerances."

I have thought about taking a dremel with polishing head and trying to increase the angle and depth of the dimple a bit, but was hesitant. Has anyone else had this problem, and if so, how did you fix it?

Try placing a few drops of CLP on the detent and working the door open and closed . With time it should loosen up.

Quoted: Try placing a few drops of CLP on the detent and working the door open and closed . With time it should loosen up.

No go. That was actually one of the first things I tried. Guess it's either testing other port doors or a light dremel job. I can't bring myself to send this one back. It's too damn good looking.

Did you hit it? Things work better when I hit them.

The dtent could be stuck or could be a defect..change the cover..the spring could be messed up.Those assemblys are pressed in anyway..no way to change it out except a new door.

Ditto what pun said.

I've tried to work on some dust covers that the detent acts like it is sitting to high.  It's just plain easier to swap the whole cover.  Sometimes it has been the diameter of the hole the detent sits it.  Too much play caused the detent to bind.

I would swap the cover first before hitting the upper with the dremel.  

In the mean time, let your thumb nail grow a bit.  As you close the cover, depress the detent with thumb nail.  That's what I do to close it quietly.  Of course optics will get in the way if you have them.

my .308 bushy detent wasn't large enough and I had door closure problems. Common oops on their part so said the guy in the shop.
I carefully touched it with a dremel and it works fine now

apply hammer. if that doesn't work, re-apply as necessary.

Bring it back and have it fixed/replaced.  If this is a NIB rifle there is no reason you should have to fix quality control issues.

DON'T YOU DARE DREMEL IT!

It's new ... like all things new, it's just tight. Just bear with it and press on the detent several times to loosen it up.

If you can't wait soon enough for it to loosen up, then just change the the ejection port cover.

Id be swapping out the door before even thinking of using a dremel on my upper.  Remember, you cant put the metal back.  Sh*t happens, and I am guessing you got a bum ejection port cover.  

Duct tape.
Damn it, the fingers just won't shut up!

Are you sure the holes on the side of the receiver for the ej. port cover guide rod are not drilled too high?

My dpms is kind of like that.  I have to shove it close with my thumb.  It's probably cause it's new.  It was really tough when I first got it.  It's not so bad now.

The upper should have a slight radius to allow the detent to close easier, is it there?

Is there a chance that the detent is sticking out too far??

Is the EPD rod bent???

There is a way to check and see if the cover holes on the receiver are not drilled right.Try pressing on the cover with out the rod and see if it lines up.

Quoted: Step 1.  Check the detent on the ejection port cover with your finger.  Does it move freely?  If not add a drop of oil and try to work it up and down.  If that is a no go, get a new cover.  I will send ya one for free.  Moves freely, detent spring tension seems normal Step 2.  If the detent is functioning check the ejection port to see if it is curved or bent.  If it has a slight curve in it, straighten it with pressure from your thumb and forefinger.  Tweak it straight.  It should close.  Seems to be straight, not bowed in or out Step 3.  If 1 and 2 fail, replace the port cover. Denny

I think the detent housing was just pressed a tad too high into the port door, or the detent is sticking out too far. That's all I can figure. I have tried all of the suggestions in this thread (most were common sense), and thank everyone for their replies. I'll just buy and install a new ejection port door.