An interesting note, IIRC, Pat Rogers was a reservist assigned to the Marine Corps foreign materiel acquisition and exploitation program and was one of those Marines who got some intimate range time with the XM4 in 1986.

IMHO, though it looks like a nice little piece, that upper looks more like a mix-master of parts than anything else to me.  

FNMI upper with teardrop forward assist and flat slip ring, with an early Colt RO723 or 727 .625 barrel is almost certainly not a factory configuration, nor an XM4 program upper.  

A lot of folks seem to be mistaking Colt commercial/export carbines, USAF or IDF mixmasters, or other carbines from the mid-1980s on as somehow representative of the XM4 or M4/M4A1 - remember that most of these developments, though superficially similar, and/or designed to retroactively mimic the features of the M4 series, are wholly separate from them.  The RO727 "M16A2 Carbine," though looking quite similar to the XM4 is in many ways only a distant cousin, not a direct descendant - GUU-5/Ps and IDF carbines are even further removed.

~Augee

GUU-5/Ps are still my favorite, AND now there ARE FN marked M4 uppers....

thanks!

found this pic online, said it was Delta in Colombia...M4 barrel, some type of A1 sighted upper...

hey Augee,  add this one to your clones

taped on maglites..

In 2002 while I was in Afghanistan, I saw a carbine almost identical to that one being used by an AF dude. I'm pretty sure he was a combat controller. He was attached to our BN.

GUU-5/P most likely

kind of on topic..an adapter on a pencil barrel to allow m203 mounting..

Looks like a 723 and an early plate carrier.

One thing specops does is burn out barrels pretty quickly, so a 723 rebarreled with an M4 barrel is probably pretty common.

As well as being built that way to begin with. A very practical, 'easy to do' build.