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9/22/2017 12:11:25 AM
Posted: 8/17/2003 9:39:06 PM EDT
I looked around for a while, but couldn't find a reference picture. I consulted my USMC manual and other reference manuals, but couldn't locate a useful picture.
On my Colt AR-15, preban with an A2 upper, I noticed a groove aprox. 1 inch rearward of the locking lugs.
This "groove" doesn't appear to be machined, it is pretty rough. It looks as if it sheered off. No damage is apparant thru the other side. I also hadn't noticed it before.

If it is supposed to be there, what's it for?
TIA,
-Steve
Link Posted: 8/17/2003 10:20:46 PM EDT
are you sure that isn't the groove for the ejection port cover's tab to sit in? this is what makes the cover open automatically when the bolt cycles - the tab gets pushed out of its groove. If not that, I don't know. Pic is kinda blurry.
Link Posted: 8/17/2003 10:35:11 PM EDT
Sorry about the pic, the camera is older than dirt. No, that groove is against the "other side" (inner port side) of the upper receiver. The groove looks as if I scooped a piece out with my thumb nail. It is at the top of the magwell, and where the upper receiver is round for the bolt carrier. -Steve
Link Posted: 8/18/2003 4:02:09 AM EDT
I think that’s simply the byproduct of a mill cut made through the magazine well and into a higher area inside the upper. Look directly above it maybe ¾ of an inch (holding the rifle horizontally) and you should see what I mean. Alternatively, look into the magazine well from the bottom.
Link Posted: 8/18/2003 12:33:18 PM EDT
Makes sense 199. I had looked at that possibility, but I would of thought they'd clean it up a little. So, yours has this thing too? Thanks, -Steve
Link Posted: 8/19/2003 2:48:47 AM EDT
Originally Posted By stevenb: ... So, yours has this thing too?...
View Quote
Yep!
Link Posted: 8/19/2003 4:10:59 PM EDT
All three of my AR-15 uppers,(Oly, RRA, and a CLE), have the same milling mark. It's just part of the design.
Link Posted: 8/26/2003 9:02:23 PM EDT
I'm a machinist, and we call that a clearence cut. None functional cut to allow a tool in for a different cutting operation
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