AR-10 clone of SR-25 MK 11 Mod 0


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


AR-10 clone of SR-25 Mk 11 Mod 0

I have been interested in the SR-25 with a particularly strong interest in the SR-25 Match rifles with the Knights Free Floating RAS system for at since early 2001. With that said, when I finally bought my big bore black rifle, I elected to buy an Eagle Arms AR-10 for three basic reasons. The first reason is the magazines, as Armalite AR-10s use modified M-14 mags that are much less expensive than the less common SR-25 mags. The second reason I choose the Armalite AR-10 is due to the ability to buy spare parts, uppers, and other components directly from Armalite while Knights has been less willing to sell additional parts or materials to owners of SR-25 as opposed to Armalite. The third advantage the AR-10 has over the SR-25 is a higher percentage of AR-15/M-16 parts which could be important in the future.

After buying my AR-10, I looked into using a Knights Free Float Rail Adapter System (KAC FF RAS) as I managed to buy one of the first Knights FF RAS Assemblies sold to the public in September 2001. As I am sure this is a month that none of us will soon forget, Knights stopped supplying the FF RAS to the civilian market as they increased their military production. The FF RAS I had bought at that time was a short FF RAS that is the same length as the standard AR-15 carbine forend.

I looked at having an AR-10 upper built that could incorporate this short free floating RAS tube but there were a number of problems that I encountered. First, the AR-10 carbine uses a special mid-length forend tube that is considerably longer than the standard short carbine forend on most AR-15s. This would have resulted in a major gap between the front of the free float tube and the front sight. The second major problem involved the barrel nut as the AR-15 and the AR-10 use significantly different barrel nuts. More on the barrel nut issue in a minute!

At this point I got frustrated as the FF RAS tube that I owned was made for an SR-15 and given the differences between the AR-10 and SR-15 barrel nuts it seemed that my only option was to extensively modify the FF RAS for it to work with the AR-10 plus build a special traditional length AR-10 carbine (as opposed to mid-length as Armalite makes). Neither of these options seemed appealing as the $500 RAS was too expensive for me to use as an experiment and moving the AR-10 gas port to a traditional carbine location would have certainly caused problems. Accordingly, my next step with my AR-10 was to mount a standard Knights M5 RAS as described on this page and save the FF RAS for another project.

Significant time has passed (September 2002 now) and it should be clear that Knights Armament has been supplying their SR-15 Free Floating RAS tubes to the market and they are appearing for sale on many internet forums and at gun shows. The Knights FF RAS Assemblies are available in several distinct sizes and styles that I describe in considerable detail in my Knights FF RAS Assemblies page.

Left: Short M4 Free Float Carbine R.A.S. (KAC P/N: 20208)
Middle: M4 Carbine RAS Assy "MEDIUM" Length KAC P/N: 20214
Right: M-4 Match/Sniper Free Floating R.A.S. Forend (P/N 99266)

I have now learned that the SR-15 FF RAS and the SR-25 FF RAS are very different tube and that the SR-15 FF RAS tube will not work on an SR-25 or an AR-10. I have moved the discussion about my problems with using SR-15 FF RAS tubes with the AR-10 to this new page.

The status of using an Free Float R.A.S. tube on an AR-10 is such that I have heard from two people that use FF RAS tubes from an SR-25 on an AR-10 without problems. I have been told that the AR-10 will accept the SR-25 parts including the SR-25 barrel nut. One area of caution should be considered however because the outside diameter of an AR-10 barrel is a little more than 1.20". The corresponding inside diameter of the RAS is approximately 1.255". So this is a very small .055 difference, but since its a diameter difference, you must divide it by 2 to determine the size of the gap between the OD of the barrel (chamber area) and the ID of the RAS; this is only .0275". That is about the thickness of two business cards. It should be obvious that this close proximity between the FF RAS and the barrel is not a good thing for cooling. In addition, this "tight" area is over an inch long on the RAS so it more or less pretty well covers the chamber area. In addition to improper cooling of the barrel which would reduce barrel life, this will also cause the FF RAS on an AR-10 to heat up more significantly then on an SR-25 rifle. Needless to say with a lighter weight/smaller diameter barrel, the potential problem with heat dissipation is reduced.

Unfortunately, as of this date (9-10-2002) Knights is sill unwilling to sell SR-25 FF RAS tubes to the general public. The general impression I get for the reason for this is that the KAC FF RAS is one of the key parts of the Mk11 Mod 0 sniper rifle system and variants that are being used by the US Military. If KAC was to supply these parts to the market, it would be easier for Armalite to make a tactical version of the AR-10 that could compete with the SR-25. KAC does not wish to provide the means for another company to make a weapon that can match their own system when if we want an KAC SR-25 with a FF RAS we can just go to Knights Armament and buy one! While I wish I could buy an SR-25 FF RAS and use it on my AR-10, I respect the reasons why KAC does not sell these tubes to the public and I continue to wait for a similar system that will work on my AR-10.

The SR-25 and AR-10 rifles are well known for their exceptional accuracy and through the addition of this versatile Free Floating RAS system; this accuracy is maintained along with the ability to add a wide variety of tactical accessories. The SR-25 Mk 11 Mod 0 sniper rifle is an exceptional weapon system that is available for a rather steep price. If Knights Armament should decide to sell SR-25 FF RAS tubes to the general public, then those of us that want an SR-25 Mk 11 Mod 0, but can't afford one, will be able to build a very good copy using either an AR-10 or SR-25 as the base weapon platform.

I close with a photo and description of an SR-25 Mk 11 Mod 0 Sniper rifle.

Mk11 MOD 0 is a military designation originally applied by the United States Navy for a sniper support weapon system based on the SR-25 and originally deployed by the SEALs. The Mk11 MOD 0 includes a 20" (508mm) cold hammer-forged free-floating target barrel, Knight's Rail Adapter System (RAS) consisting of four Picattinny rails for mounting various devices, flip-up front and rear detachable iron sights, Harris swiveling bipod, a Leupold 3.5-10x40mm variable power scope with mil-dot reticle, heavy duty scope mounts and a Knight's SR-25 Quick Detach sound suppressor offering -28dB of noise reduction. This rifle is also guaranteed to shoot 1 MOA but many shoot far better than that.


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This site was last updated 02/28/03