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Knight's Armament Co URX 4 Free Float Rail System for M4 / M16 Series Airsoft AEG Rifles (Length: 13")

ID: 53768 (RIS-KAA-URX4-13)
Knight's Armament Co URX 4 Free Float Rail System for M4 / M16 Series Airsoft AEG Rifles (Length: 13)
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MadbullKnight's Armament Airsoft

$85.00 $55.25

MAP ProtectedExempt From Coupons
The manufacturer of this product enforces a strict minimum advertised price (MAP) policy which excludes this product from any additional discount coupon codes. This item, however, may qualify for free shipping.
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The KAC URX 4 Rail is a fully modular design that utilizes the revolutionary KeyMod accessory mounting system. The URX 4 Rail is stronger and more stable than previous URX designs due to its one piece construction. It is also lighter due to its Integral Barrel Nut (IBN) system of attachment. The IBN system allows the rail itself to act as the barrel nut when torqued onto the rifle, completely eliminating the need for a separate steel barrel nut. KeyMod accessories may be mounted anywhere along the URX 4's length, making it one of the most user configurable designs on the market.


  • Fully licensed by Knight's Armament Company
  • Made from CNC milled aluminum
  • Matte black anodized finish
  • 20mm Picatinny top rail
  • Compatible with airsoft spec. KeyMod systems
Length: 13"
Compatibility: For Tokyo Marui, Matrix, G&P and other compatible M4 / M16 Series Airsoft AEG Rifles
Material: CNC Milled Aluminum

Manufacturer: Knight's Armament Co.

About Madbull

MAD BULL Airsoft, established in 2004, is world famous for it's Airsoft accessories. Our major focus points are: Airsoft guns, Airsoft Toy Launchers, Airsoft Toy B.B. Showers, and Upgrade kits.We have a very strong R&D team and we put a lot of effort in designing new and exciting new products for the airsoft community.

6 Customer Reviews

(Write a review)

by Grant W. on 11/22/2016
"Absolutely fantastic rail. I was a big skeptical at first because the whole rail screws on to the receiver, but it also has a little bar where the gas tube would normally go that can be pushed into the receiver's gas tube hole and then tightened down with hex wrench from the top. It's extremely sturdy and lightweight. Also, I have a 38mm diameter suppressor inside mine right now and it fits just fine, although I don't think there's enough space inside the rail for keymod attachments. I'd say the absolute maximum size suppressor that would fit inside the rail is around 40mm in diameter.

One con: The rail still needs to be tight in order to hold the outer barrel steady, but mine came with a few small shims/spacers and two larger ones. I needed a spacer that was thinner than the large ones but thicker than all the small ones put together. I ended up having to grind down one of the large ones till it was the right size.
by Dalton P. on 02/25/2016
"I got this system for my G&P WOC gas blowback rifle and it actually fit. I really had to work in the threads for an hour or so but no damage came to either the guns threads nor the rail system, it was just a really tight fit. I did use a rubber mallet and a screwdriver but now I can screw it on with my hand with no issues. The rail system looks great, it feels solid, it's stupid simple, and it's just overall a good product. One thing that I guess is noteworthy is that the rail system is about a half millimeter taller than my WOC's upper receiver rail, but it's basically unnoticeable unless you're looking for it. Also if you're looking to integrate a suppressor underneath this system, the diameter is 40mm by 40mm so use a supressor that just a bit smaller in diameter and you should be good to go.
by Kenneth L. on 05/29/2015
"I got this today and I have to say it's incredible!! It is lightweight, tons of Keymod slots, and you will have a monolithic upper rail with any Madbull M4 receiver.

- Knights Armament Co trademarks.
- It DOES accept Mil-Spec and airsoft keymod picatinny segments.
- Exact replica of real steel counterpart.
- Lots and lots of keymod segments.
- Super easy installation (literally screw it on the upper receiver).

- It took 30 mins to install because it came with 3 different sets of barrel spacers which you have to decipher what set of spacers works best.
- You will need either a KAC URX torque wrench or a towel and mallet to tighten the upper with the rails.

I highly recommend this rail to anyone who wants something more of "your own taste" in accessories placement arrangements. It gives a whole new tactical look to your gun, and its just super awesome!!

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