Here is a cut and paste from the JT sight.
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COLT M-4 Upper with Swivel
ALL COLT! Flat top with carry handle, bolt assembly, M-4 handguards and sling swivel attached. Upper receiver, with bolt assembly, adjustable rear sight, delta ring assembly, forward assist assembly, and gas tube assembly..
- - - $749.95
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Go to the bottom of their start page, and click on the Specials. I swapped a couple of Emails with them, and they told me the uppers were untouched from Colt. As long as they have the markings and the feed ramp cuts.......
BTW, My 6920DC has a 1/7 barrel on it, and I know it is all Colt. I think the 1/7 will be just fine for my intended use.
Good luck,
Joe