AR-10 Rail FF Tube


Up one level
SOPMOD M4 Carbine
KAC Free Float RAS
KAC 2-Stage trigger
Knight's SR-47
Knight's SR-25K
M5 RAS on AR-10
AR-10 Rail FF Tube
M5 RAS Dissipater


The Mil-Std-1913 AR-10 Free Floating Forend tube

A product many of has wanted for way too long!

NEW UPDATE!  These Rifle and Carbine tubes are now for sale!  Please visit  and tell them that Quarterbore sent you!

My Review:

Where does a person start when talking about the AR-10 railed forend tube? Well, I suppose it best described by looking at the Free Float RAS tubes built by Knights Armament that have been a popular item with the Military and Civilian enthusiast for several years. Personally, I remember the days when Knights Armament was not selling any of the FF RAS forends to the general public. I was so desperate that I searched the Internet long and hard and was extremely excited to have the opportunity to purchase a used take-off Full Length Free Float RAS from a Knights Armament SR-15 Match Sniper rifle. Back then (Fall 2001), I paid $500 for the tube and I was quick to place this SR-15 FF RAS onto my Pre-Ban Bushmaster using a Douglas 1:8 twist DCM profile threaded barrel to build my own version of a Special Purpose capable Sniper quality rifle. The rifle shot extremely well and it was my pride and joy for quite a few years.

As time went on, Knights Armament decided to release their various RIS, RAS, and free floating RAS tubes to the public and the value of my tube dropped from $500 to about $300 today. Ever sense Knights Armament started selling the SR-15 FF RAS to the general public I have been an active proponent of KAC doing the same with their SR-25 FF RAS. The SR-25 FF RAS is a considerably larger unit that serves the same function as the SR-15 FF RAS but Knights Armament restricts the sale of these units to their own SR-25 rifles.

Now, we might speculate on why this is but I assume it should be clear that Colt and FN are two of the larger suppliers of M-16s to the Military and by supplying the FF RAS to the government and the civilian market KAC generated considerable sales which likely didnít the sale of their own M-16s. When it comes to the SR-25, Knights Armament has several extremely accurate and well designed sniper rifle systems that rely on the SR-25 Free Floating RAS to give their rifle a solid advantage in the field. An example of this is the SR-25 Mk 11 Mod O Sniper Rifle System as in the following photo.

Given that the SR-25 is the premier weapon in the military arsenal it should be clear why KAC was not at all anxious to sell their FF RAS to the military or the civilian markets. I make this statement as the Armalite AR-10 has a few advantages when compared to the SR-25 and Knights Armament needed to preserve the advantage they possessed in their special purpose Free Floating Rail Adapter System Forend. 

Well today, 29-Oct-2003 I have received an item that I am extremely happy and honored to have the opportunity to review! This story goes back for several years with myself and others that seem to live on the internet forums trying to promote the idea of a Free Floating Forend system for the AR-10. I remember at least 2-years ago I first learned and then figured out how to mount an M-5 RAS (non-Free-Floating) on my Eagle Arms AR-10A4 and the upper really looked very good but it just lacked the free floating character that really makes the Stoner platform shine as an accurate weapon system. Over time, many of us have asked Armalite, ARMS, and even Knights Armament to make and sell us a system for the AR-10 and SR-25 that would free float the barrel and allow us to add the various Modular Weapon System (MWS) accessories via a Mil-Std-1913 rail.  This same system is extremely common with the AR-15 platform and literally dozens of different versions exist but nobody had previously offered to move towards making railed tubes for the AR-10 and SR-25 in any large scale.

This leads us to a couple discussions that began on the premier website for the AR-15 enthusiast, These discussions began a couple months ago where one guy started working on some plans and considerable interest was expressed and eventually a second individual who had access to a full machine shop and a CNC mill took the initiative to give us what we have been looking to buy.  In the following photo  you can see a new Mil-Std-1913 AR-10 Float tube shown above a standard Eagle Arms AR-10T Free Float tube.

 Following are some photos of this new tube along with a few details.  I will work on getting better pictures outside as interior light just doesn't really do great with digital cameras but this really does give you the basic idea on what this new tube is all about!

Top:  Eagle Arms AR-10T

Bottom:  Colt M4 Carbine w/ KAC FF RAS

Across the AR-10 FF tube

Across the AR-15 FF RAS

Height of AR-15 FF RAS

Height of AR-10 FF Tube

Muzzle end of AR-10 tube

Receiver end of AR-10 tube

Threads of AR-10 tube

AR-10 tube next to AR-15 FF RAS


Eagle Arms AR-10T free float tube above the new Mil-Std-1913 free float tube

Removing the gas block

Removing gas block (cont)

Removing gas block (cont)

Gas block and gas tube removed

Removing the handguard retaining nut (Note, needed a strap wrentch)

Removing the factory float tube

The AR-10T Barrel nut inside the handguard retaining nut.  Note, the barrel nut did not need to be touched at all!

Left:  Eagle Arms AR-10T float tube

Right:  New Rail Forend Tube

Left:  Eagle Arms AR-10T float tube

Right:  New Rail Forend Tube

Left:  Eagle Arms AR-10T float tube

Right:  New Rail Forend Tube

Top:  New Rail Forend Tube

Bottom:  Eagle Arms AR-10T float tube

Top:  New Rail Forend Tube

Bottom:  Eagle Arms AR-10T float tube

First, slide gas tube through the barrel nut

Then tighten the handguard nut down to secure forearm.

I tightened this a little bit with the strap wrench to make it snug,

The gas block after tightening it down again.

Gas block & forent tube

Screwing in a front sling mount

Front Sling point tightened down

The rail was perfectly straight and aligned with the upper receiver (Left to Right)

The top of the forend rail is exactly the same height as the upper receiver!

The AR-10 with a Mil-Std-1913 Free Floating rail above my M4 Carbine with Knights Armament Free Floating RAS!

A dream come true!

A dream come true!

A dream come true!

A dream come true!

A dream come true!

A dream come true!

Well, at this point I need to close this review with the promise to take some additional photos outside where the true beauty of this float tube can be appreciated. 

Update19-Nov-2003!!!  This Tube and a Carbine length version is now for sale!  Please visit  The carbine length tube is the mid-length that a AR-10 carbine owner needs and following are a couple photos of one of the carbine tubes in "the white" waiting to be anodized!

above:  Top View:

bellow:  Side View

I wish to thank Art for making this product for all of us AR-10 owners that have begged Knights Armament to sell us their SR-25 FF RAS for years.  These new tubes provide the AR-10 owner the versatility that the AR-15 platform has enjoyed for several years on the big black rifle that really does benefit from a solid free-floating assembly that is rugged enough for us to attach items of interest.  I see this carbine tube plus the prospect of a new collapsible stock as being a great new weapon system for the Military as well as police where a light and powerful weapon system is needed and with these rails lights, lasers, and other tools of the trade can be added to the black rifle with a 308 inside the magazine! 


Home | 300 Whisper Pages | Knights Armament | AR-15 & M-16 pages | My Projects | Knife Pages | Timeshare Page | Library | Online Store | Links | About Me | Webpage Updates | Contact Us!

This site was last updated 03/24/04