Now that the URG-I is evidently rolling out to US Army Special Forces Groups, I thought I’d do a quick primer on it.

A collection of Block II M4A1s with URG-I parts fitted


So what is the URG-I? Is it “Block 3”, or maybe “Mk18 MOD 2”?

Not quite. URG-I stands for Upper Receiver Group, Improved. This is not to be confused with SURG, which is a separate programme:

SOCOM’s SURG winner from Sig Sauer

Current public URG-I reference pics show an array of improved parts, used to outfit existing M4A1 long (14.5″ barrel) uppers. These improved parts have been spec’d specifically for USASOC – which stands for US Army Special Operations Command. This is a particular Army command and therefore does not span the whole of SOCOM.

USASOC’s elements (some of whom already have the URG-I) largely use the M4A1 with the Block II accessory package. Therefore rifles which utilise the URG-I are still Block II.

Keeping Up To Date With Developments

The very best resource for learning about the URG-I and how to clone it is this thread on It’s very long but it goes into way more detail than this primer will.

If you keep tabs on it, you’ll usually see new URG-I reference pics and discussion there first – well before the IG sharing pages – although @btl_ltw on IG is also fast and reliable.


Because the thread is trustworthy, I’ll directly quote the 14.5″ URG-I setup recommended:

Lower Receiver Group

Lower receiver – M4A1

Receiver extension – standard M4/M4A1

Action spring- standard M4/M4A1

Buffer – H2

Grip – standard M16A2/M16A3/M16A4/M4/M4A1

Stock – SOPMOD

Trigger- Geissele SSF – P/N 05-102

Selector- Colt full auto ambi – P/N SP401017

14.5″ Upper Receiver Group, Improved – NSN 1005-01-671-3911

Upper receiver- standard M4/M4A1

Bolt carrier group – standard M16A4/M4/M4A1

Charging handle – Geissele Airborne Charging Handle in Desert Dirt Color with subdued markings- P/N 05-664S – NSN 1005-01-672-4803

Barrel – Daniel Defense 14.5″ mid length “GOV” profile with .076″ gas port – P/N 07-077-07308

Gas block – Daniel Defense pinned gas block which comes on their rifles and URGs

Gas tube – Daniel Defense mid length – P/N 04-013-18034

Hand guard – Geissele 13.5″ MK16 in Desert Dirt Color- P/N 05-650S- NSN 1005-01-672-4794

M-LOK rail section – Magpul 7 slot aluminum – P/N MAG582-BLK

Sling mount – Magpul QD- P/N MAG606-BLK

Muzzle device – SureFire 4 prong flash hider – P/N FH556RC

Suppressor – SureFire SOCOM in Dark Earth – P/N SOCOM556-RC

Rear BUIS – Matech

Front BUIS – Knight’s Armament Front Flip Sight in Taupe P/N 99051

Interestingly, the thread lists the 11.5″ version of the URG-I as “issued”, although I haven’t seen any pics of it yet.

It is not suggested that a 10.3″ version has been issued, however.

Reference Pics

Here’s a select few pics of the URG-I in the wild. Note how varied the setups are, because this is not a new rifle – it’s an enhancement of an existing one.

All pics are from the thread and @btl_ltw


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