Here's what I have:

Fixed carry handle A2 upper marked with C and MB on the right side of the handle near the rear sight. There is a small "4" on the front of the upper receiver above the slip ring.

16" Colt M4 profile 1/7 bbl w/ feed ramps marked C, MP, 1/7, 5.56 NATO.

FWIW, double heat shield handguards.


Background:

I purchased it in 1998 or 1999 and it was sold to me as a Colt 16" M4 upper. It was originally purchased through RGuns.

Questions:

Did these uppers ever come on a production rifle? I can't find any reference to either a 16'' Military M-4 or a commercial model with a fixed handle.

If not, were they made by Colt or were they Colt parts assembled by someone into complete uppers?

Any info would be appreciated.

Way back Colt made a AR6620DC conversion upper
which is the upper you describe, no chrome bore and came with an M16 bolt carrier

Not a production rifle but a production upper