Quoted:
What is a URX?? What does it do? Why is everyone so hot and heavy over it?
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When we (KAC) started working on the "monlithic UR" that USSOCOM (via Crane) said they wanted (about 3 years ago), we immediately looked at, and built some concepts similar to LMT's. However, as we looked at the life-cycle cost to the user over a 5 to 10 year period, we felt that not being able to share supply system commonality/interoperability with the more expensive components such as UR's, barrels, gas tubes, Armorer Training, TM's, etc., we developed the URX as a more cost effective solution.
URX (actually URX 4X4) stands for Upper Receiver Extending 4-Rail FF Barrel Forend.
With this design, you use the common UR, barrel, gas tube, etc., but the URX screws onto the UR as does the current barrel nut. So when the barrel is then inserted and the actual barrel nut installed, this action locks the 4x4 forend rail in alignment with the UR.
Another feature of the URX is that the lower rail is removeable to allow the user to clean around the barrel.
This design makes it impossible for the Operator to remove the upper 3 rail portion of the URX forend. This eliminates wear & tear on the "retunr to zero" interface surfaces which is may happen over time with RIS and RAS securing designs if the users too frequently remove the uppers for cleaning. I have seen RAS's in Ranger units that have had their rear clamps actually removed by a former Operator to make field stripping/cleaning around the barrel easier. However, the current user didn't know anything was missing. All he knew was that the RAS was not as secure as he wanted it to be. So URX eliminates this possiblity while allowing access for cleaning, attaching a grenade launcher as close to the host weapons barrel, etc.
Although I like LMT's design, I know that Military Armorers would rather have a footlocker full of complete UR's with various barrel lengths than bunches of separte barrels, gas tubes, small parts, tools, workbenches, etc.
I saw an Army Diesel Mechanic interviewed on a morning talk show a couple weeks ago. The interviewer was impressed that this pretty female Soldier was indeed a Diesel Mechanic, and asked her how many vehicles she had repaired since deploying to Kuwait and onto Bagdad. Her answer was "none." In fact she said she had not seen her tool box since Fort Bragg. So then he asked her, "well just what have you been doing." Her answer, "I am the .50 Gunner on out 5-Ton" (truck).
So you see that in actual combat, many Combat Service Support Personnel who follow in trace of the lead elements in what the Army calls the "Trains", end up primarily employed in secondary roles like Gunners, Drivers, etc. Then when the advance stops, then they may set up shop, but only after securing a site, developing a defensive plan, standing guard duty or "hole watch".
SO an UR module that only requires the Operator to push on two pins to switch from one barrel length to another seems to be the more practical and fail-safe way to field and forward deploy such a "multi-barrel" concept.