I know this is kind of a weird question, but bear with me.  

I just received a new Colt M4 upper (properly marked) and I noticed a bit of milling that wasn't completed.  There are two "channels" (for lack of a better word) that run beneath the rail where it meets the upper.  They are about 1/4" wide and run the entire length of the upper.  They are very shallow.  One of these "channels" wasn't milled on my upper so it is raised as opposed to being sunken.  I'm not too concerned about it persay, but I'm wondering how this could be missed and is it possible that it wasn't completed because it's a factory reject.

Could be, there's been a lot of odd Colt marked stuff showing up. I'd return it to the vendor, after contacting them first of course. Mind telling us where/who you got it from?

I was afraid somebody was gonna say that.  I got it from Kyle Armament.

Here are a few more oddities.  On the left side (opposite the foward assist), there is a place where it looks like some filing was done before the receiver was anodized.  It is about 2" x 3/4".  It's very smooth, but you can see some definite lines.  Also, the forward assist looks like it was finished with a file.  It's not smooth at all.  It looks very similar to the forward assist on the upper in the picture below.  My C AF looks a little different, too.  The C is more closed than the one in the picture and the C AF is lower...at the bottom of the flat.  The edge of the ejection port is not very smooth either.  It has kind of a wavy appearance all the way around the inside edge.  The milling inside is flawless.

Here is a picture I got from Biggerhammer.  It has the same marks on the forward assist as mine does.

[img]http://www.biggerhammer.net/ar15/uppers/colt_flattop_proofmarks.jpg[/img]

I had a Colt that had those exact marks too. A fellow I shoot with wanted it just because it said Colt and traded me a flawless flat top upper from RRAs that matched my lower better. Just because it is a Colt don't make it perfect at all. I would see if the vendor will replace it.

IPSC_GUY sends

Anybody think Colt would exchange it?

Could be someone is selling Colt's rejects as new parts?  

-- Chuck