Original Sniper/Recce Carbines were 723s free-floated with KAC 2-stage triggers, suppressed. Early 1990s after Panama. LAV talked about it in an article several years back. They started shaving carry handles off after seeing the Colt ACR submission, which happened in the 1980s.
Guys started asking for more accurate pipes, so they tried stainless match, but those shot out too fast on the Unit shoot schedule, so they went back to CMV pipes instead to increase the intervals of barrel change.
Assaulters were having barrels changed every 2 weeks just for reference.
They started out using 14.5”, while some 16” were used later.
Dam Neck guys saw them and wanted something similar, so they sourced Lilja pipes for their 727s and used free-float handguards as well. By the time Navy SMU started doing them, the M4 had just gone into production, so there were some early transitional Recce carbines that took the barrel, aluminum free float tube, and suppressor combos from the 727s and just had it all mated to an M4 upper.
Those evolved into these:
In the Army SMUs, it became the KAC MRE Recce:
Biggest departure from the concept it weight and barrel length. The whole idea was having the same basic weight as a 723 Carbine but accurized, better trigger, with magnified optics mounted and useful Night Vision/Own the Night accessories. If a Sniper needed to switch to assaulter as part of contingencies, he could still do so without being burdened with an SR-25 or M21 and would share ammunition compatibility across the element.
The SPR in SOCOM was an out-growth of this initiative that started in the Unit. If it’s going to be suppressed, you can get rid of some barrel mass and let the can act as a heat sink to some extent. I really like how pencil weight barrels feel under a free-float, but not how they walk around after half a mag at 400yds.
The Mk.12 Mod H was an attempt to get back more to the somewhat-practical carbine configuration that existed from the start.
Main takeaway is that training, free-float, optics, NV-capabilities, and match ammo were more important for the Recce Carbine formula. A lot of the AR-15s on the market loosely follow this recipe without the manufacturers or builders being aware of the true origins and why.
there’s a lot of great manufactures mentioned here, but after speaking with Paul at Craddock, I pulled the trigger on this guy:
www.bonesteelarms.com 
( I mean we all do from time to time)
). A 20 inch rifle gas would be exactly what I need for a build I have in mind.
riflebarrels.com
