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?