A Look at the Geissele Automatics URG-I

URG-I close

Let’s get straight to it: “URG-I” stands for “Upper Receiver Group — Improved.” It’s the “new” M4.

The URG-I is available from Geissele Automatics (pronounced “guy-SUH-lee”) as a complete upper assembly (not a complete gun). 

The URG-I resulted from a United States Army Special Operations Command (USASOC, no more “SOCOM”) contract project.

It was completed and released mid-2018, and I got mine in early fall of that year. 

URG-I: A Mercifully Short Back-story

Any “new” AR-15 isn’t really new. It’s another version of the original.

It’s been 60 years since its inception in 1959 (with the Model 602, the first ArmaLite AR-15 actually sold into service).

If there’s an ongoing theme with this series, it’s “evolution” — change, improvement, refinement, repurpose.

This is made more easily possible by the whole “modular” nature of the design.

The first “shorty” experiment was the Model 605, a rifle with its barrel shortened to end just at the front sight housing.

After more mods came the Model 609, it became the first carbine to see wide-scale production and use by U.S. Forces.

It entered service in 1966 designated as XM177E1 (“XM’s” and “E’s” denote “experimental”).

It also had the “second-generation” stock, which was the now well-known collapsible style we’ve come to associate with this line.

This platform continued to evolve throughout the course of the Vietnam conflict (with 15 unique model numbers).

A main (and eventually defining) change was a move to a 14.5-inch barrel (10 and 11.5 lengths preceded).

The 16-inch “standard” for a civilian AR-15 carbine came from the need to comply with NFA regulations.

URG-I upper overall
All genuinely-genuine parts: Colt’s, Daniel Defense, Geissele, Sure-Fire. The rail is proprietary to the URG-I. Super-slim and with Magpul M-LOK accessory mounting slots. The Airborne charging handle is just plain nicer to use than a standard form, and it’s stronger. The mid-length-positioned gas block is permanently located via a 3/16-in. split pin.

The M4 came to be in 1994. That was another evolution of the carbine and the essential goal was to increase its effectiveness and versatility.

The goal was for its capability to be more of a soldier’s “main” battle weapon.

Since then, there has been a multitude of detail changes and I count eight definable M4 variants. 

URG-I is the latest. 

URG-I Highlights and Features

Components of the URG-I include:

  • Colt’s Mfg. M4 upper receiver and M4 bolt carrier group (both true-issue)
  • Daniel Defense hammer-forged barrel, 14.5-in., 1-7 twist, NATO chamber
  • SureFire SF4P flash hider
  • Geissele MK16 Super Modular Rail, 13.5-in.
  • Geissele Airborne charging handle.
  • Geissele gas block, pinned. (Mid-length gas port location.) 

That last is a big deal. The biggest functional difference between the URG-I and previous M4s is its relocated gas port.

Moving the port forward a couple inches (from seven to nine) results in a relatively huge reduction in gas port pressure.

No room to elaborate fully (that’s in another article), but an overage of pressure entering the gas system results in a wholesale acceleration of action function.

The bolt tries to unlock too quickly, then excessive bolt carrier velocity follows.

Overactive cycling creates numerous undesirable effects, and familiar tricks like heavy buffers and adjustable gas blocks seek to abate that influence.

The best solution (always) is to move the gas port forward. The closer the port is to the rifle chamber the higher the port pressure will be, and vice-versa. 

URG-I 602 clone
Next to my 1959 602 clone, the URG-I is a good example of the design refinement that’s kept this whole platform in service this long. Tops and bottoms still swap!

The URG-I got the relocated gas port primarily to handle the extra pressure of the mil’s newest ammo, M855A1 (AB57).

“Real” NATO ammo is hot and getting hotter. Figures I’ve seen show AB57 between just shy of 62,000 PSI to nearly 63,000 — vastly more than “old” M855.


One point on the wishlist for M855A1 was 20-in. barrel velocity from 14.5. 

Think of the gas system as a pressure chamber with two valves — one at the gas port and the other at the muzzle, and the moving bullet opens each as it crosses each plane.

As started on, more bore volume before the gas port means less pressure at the port.

Post-port barrel length influences how long the system is under full pressure, and the shorter the length, the shorter time, and that’s better — if we’re dealing with higher-pressure ammo. 

URG-I hornaday black
As I first set it up, URG-I gas system architecture did not run with commercial-spec .223 Rem. ammo. I got out some factory “match” ammo for a fair test of its group potential. Bang! Click. Not enough pressure to cycle. The mods are that effective. Runs perfectly with Hornady Black. Buffer system changes later let it run with lower-pressure ammo.

The commercially available URG-I has a permanently attached flash hider, so barrel total length complies with NFA 16-in. minimum regulation.

It’s expertly pinned in place. Nice! Plus, of course, the overall length reduction is an advantage in handling.

The SureFire SF4P flash hider is a proven “twisted helix” design and very effective.

I’m a fan of Geissele handguard rails and will use one for a build when I can (they only install correctly on a USGI-pattern upper).

The proprietary MK16 rail developed for the URG-I is their slimmest yet (1.58-in.).

Geissele rails are well beyond “sturdy,” and have a great feel (that’s why I use them) and, for DIY builders, they also provide about the most straightforward installation on the market. 

Getting It Done, and Out

After gaining some insight from those who knew, I finished a lower for it that closely mimics the issue USASOC gun. Details nearby. 

Total gun weight, no sight: 6-lb. 9.5-oz. Nice. 

URG-I lower parts
I finished off the URG-I with my USGI-standard go-to Fulton Armory lower (genuine-contractor-produced) full of suitable-same pieces-parts; Geissele Super Tricon trigger (a semi-auto version of their in-issue SSF); B5 stock and grip (also in service); Geissele Super 42 buffer system (intended for use with this upper).

So, how’s it shoot? Very well! It’s as soft-shooting as any carbine I’ve yet fired, including my modified guns.

The URG-I gets its good manners “naturally.” With what I call “good” factory ammo, my URG-I groups a reliable 1.5 MOA, minus.

I say that’s great, and also that it’s not a bag-rider.

As I finished it, it’s got a great balance and a very good trigger, mounts up quickly on point, and I can drive it target-to-target like it’s programmed — very easy to hit with.

Compared to a routine carbine, there’s a whopping lot less firing-induced sight displacement. I bolted on a Burris AR332 (good sight, great value). Was fresh out of Mil-Spec ACOGs…

What’s It Matter To ‘Us?’ 

Look over its spec sheet and you’ll see that this URG-I can effectively be duplicated (for the most part).

The parts that make up this upper aren’t cheap, but most are available, and more are available as functional alternatives.


There’s a step between mimic and mirror. One trick is finding an NFA-legal 14.5-in. barrel.

Certainly, permanent muzzle device attachment is not a new idea, but take great care to find a correctly done installation (on a good barrel).

urg-I front close
Sure-Fire SF4P “SOCOM” flash hider expertly permanently attached. 14.5-inch rifled section, 16-inch overall.

I’ve been at this a while, and “this” is being a huge fan and follower of AR15-platform firearms.

I got my first in 1975, a Colt’s R6000 (SP1). In that day, and for a good many days after, that was the only way a civilian could get hands on one.

Colt’s owned it completely. My R6000, at that vintage, had some of the “upgrades” that had been incorporated into the issue M16s through the 1960s, but it was missing the forward assist.

I wanted the doggone forward assist so it could be “the same as” the issue rifle, well, of course also accepting that it didn’t have three selector stops.

URG-I with standard carbine
URG-I along with another of my takes on an “ultimate” carbine. These both have mid-length systems, but because of the 16.5-in. Krieger barrel on the black gun, the URG-I shoots softer because of its 14.5.

Silly as it may seem, the authenticity mattered to me. 

This article isn’t about that rifle, but it is about that idea… 

And that’s why it was and is a very big deal to me to get this URG-I. The only difference in “theirs” and mine is that they don’t have to get the flash hider pinned. Technically, Geissele calls the commercial version a “near-clone.”

URG-I cost: about $1500. Worth it? If you want The real deal, yes.

What do you think of the URG-I? Let us know in the comments below!

About the Author:

Glen Zediker

Glen Zediker is the owner of Zediker Publishing, which specializes in books and other publications focused primarily on AR-15s, handloading, and shooting skills. Since 1989, he has authored or co-authored 20 books.

He started shooting at age 5 and competing in NRA Smallbore rifle at age 8. He got his first AR-15 at age 15 and has now had 45 years of experience with that firearms platform. He’s worked professionally with some of the greatest shooters on the planet and leading industry professionals. And he does pretty well on his own! Glen holds a High Master classification in NRA High Power Rifle and first earned that using an AR-15 Service Rifle. He’s also competed in many other forms of competition, including USPSA, Steel Challenge, Silhouette Rifle and Pistol, Bullseye Pistol, ISSF Air Rifle, Practical Rifle and shotgun sports.

Since 1986 Glen has been a frequent and regular contributor to many publications, having had over 500 assigned articles published. See more at
The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (5)

  1. I too am building a URG-I. My issue is locating a SF4P. You refer to it but the picture is a SF3P called every dealer and Surefire to no avail. But can’t wait to try it. I have everything except the flash hider. And recommendation for locating one would be appreciated.

  2. SJ, I was also one of the first to handle the AR15. I remember USAF Basic, we went into the training room and seated at a desk with a “toy plastic rifle”. I remember telling the guy next to me, “this must be what they use to train us on and we will get the “real rifles” on the range!” He agreed. Boy was I surprised! At least I shot Marksman on the range. As far as the “OFFICIAL” position( that the operator did not maintain the weapon correctly), maintain it with what? No cleaning supplies were issued with them! I know of men who wrote home to have their dad/wife send them their cleaning kit and carried an extra boot lace and a piece of wire cut from a fence until they got their kits from home. But he Comic Book cleaning instructions were cool. I wish I had kept mine.

  3. “I finished off the URG-I with my USGI-standard go-to Fulton Armory lower (genuine-contractor-produced) full of suitable-same pieces-parts; Geissele Super Tricon trigger (a semi-auto version of their in-issue SSF); B5 stock and grip (also in service); Geissele Super 42 buffer system (intended for use with this upper).”

    I want to build out my new milled-out lower with all these parts before getting this upper, to make sure everything fits. Can you tell me if all the parts above are in the Fulton Armory Kit (kind of the way it reads), or is this 4 separate items I would buy individually? I already have a great Geissele flat trigger for my old Busshie Dissipator carbine (definitely over-gassed), and love the 3.5lb break and general quality, so am biased towards this company.

    Thanks for the great review and any info.

  4. Congratulations and happy that you like yours. My experience as a user was not a happy one. I was issued one of the first AR15’s. And I put too many people in body bags with their cleaning rod stuck down the barrel to have any fond memories of the AR15. Following the years later tests that the government conducted didn’t show any improvement in reliability in a sustained firefight. Given that few civilians or hunters will have to fire more than 8000 rounds at a single encounter, a AR15 in whatever model is adequate for their needs.
    Its interesting to note that the “official” position on the AR15 throughout its life has been that the operator did not maintain the weapon correctly.

Your email address will not be published. Required fields are marked *

Your discussions, feedback and comments are welcome here as long as they are relevant and insightful. Please be respectful of others. We reserve the right to edit as appropriate, delete profane, harassing, abusive and spam comments or posts, and block repeat offenders. All comments are held for moderation and will appear after approval.