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


Knights RAS II

After the development of the RIS and RAS units and the Free Floating RAS systems Knights Armament set about making a new RAS assembly that is referred to as the RAS II which was shown to the SOPMOD II Conference at Ft. Benning in 1999. KAC RAS II Prototype Model

Click any of the above images for a larger image!

The prototype RAS II as shown above uses KAC's patented rear clamp on the back of the top rail that locks the whole assembly to the barrel nut. The extension that covers most of the upper receiver rail has a single "rail grabbing" clamp that keeps the rails in alignment with the upper receiver's rail. There is a second model that extends all the way to the rear of the upper receiver rail that incorporates Knight’s 200-600 meter fully adjustable flip rear sight. The model shown here, the shorter RAS II, gained the most interest because the users at Ft. Benning were use to the 300-Meter fixed range rear folding sight, which worked well with the shorter RAS II.

Advantages of the KAC RAS II include the ability to tighten its rearwards mounted barrel nut clamp with an allen wrench. This provides considerable strength if you are going to really push/pull on the vertical grip. This design also allows the M4 barrel to be free-floating. Free-floating, however, has very little benefit if shooting military M855 "green tip", which are not very accurate. There is however an increase in accuracy when commercial match grade ammo is used.

The top rail in the prototype was higher than the current M4/RIS/RAS combination, so a 4-power ACOG Scope will mount too high to be used with an M68 Reflex (unless you use a special low-profile 30mm Aimpoint mount that Knights manufactures).

The RAS II lower is really the unique part as it interlocks forward with corresponding upper assembly slots, then pivots up and engaged by the delta ring. At the rear, the RAS II is further secured by another clamp that is engaged to the barrel nut similar to the one at the rear of the upper rail. With both clamps in place, the RAS II is a very solid arrangement. One disadvantage of this two-clamp system is that this requires a 1/8" allen wrench to remove the clamp. The solution to this is to not use the lower clamp if one wishes to quickly mount an M203 or under slung 12Ga. like Knight’s Masterkey.

This style lower is so secure that it has used with the standard RAS as well as described in this document from KAC. In fact, this lower was requested by the British SAS for their version of the M4 RAS (1,300+) purchased last year (2001) for their Canadian Manufactured M4's. The SAS engage the new lower's clamp because they use H&K's new 40mm under slung, so have no need to quickly remove the lower. I have This brings up a good point if you believe in following the trend set by professions and if over 110,000 U.S. servicemen (including Navy SEALs, Army SF, Rangers, USMC Force Recon, etc.) and now one of the other "most elite" counter-terrorist units in the world (British SAS) are using a RAS, what does that tell you?

Following is a picture that shows the various parts of the Prototype RAS II system.

KAC RAS II Prototype Model

UPDATE: Sept 9th, 2002

I have just read that Knight's will probably be shipping the RAS II units to dealers by the end of September 2002! Wes Grant of M.S.T.N. is reported by Dave Lutz of KAC as having several on "Official Back Order status" as of this update. The final configuration was designated and the new assembly has a part number (22243).

Changes from the prototype pictured above include shortening the rearward extension over the upper receiver rail. In the original design (as pictured at the beginning of this page), the entire top rail surface was higher than the upper receiver's Picattinny rail. This made mounting the 4x ACOG and other fixed mount optics too high. The final RAS II (refer to image that follows) leaves enough real estate at the rear to fit the ACOG on the original upper receiver's rail (3.5") even with a KAC 300 or 600M Back Up Iron Sight (BUIS) mounted. Obviously, more real estate is available at the rear if no BUIS is mounted.

The lower of the final RAS II also includes the barrel nut clamp as described above so that the entire assembly remains very rigid, especially if the forward pistol grip is used aggressively. Dave is currently drafting the Installation Instructions and I have E-Mailed him a request to provide these for everyone's reference.

Following is a few images of the KAC RAS II!

KAC RAS II Production Model

Note in the image above that the RAS II allows normal 4x ACOG scope and simultaneous 300 Meter or 600 Meter Flip-Up Rear Sight mounting. It may also appear in these images that the forward section of the RAS II was "lowered" as compared to the prototype. Please be advised that the prototypes were this same design except in the photos of the prototypes above a removable rail is mounted! This lowered rail section is about 4.75" (or 12 accessory grooves) and is the same height as the upper receiver's rail. The lower height of this section of rail is designed to allow use of the front sight when a PEQ-2 is mounted.

KAC RAS II Production Model

In regards to the higher “Midsection Rail” section, KAC recommends using a Low Profile Aimpoint Mount (P/N: 99430) on the as shown in the picture below to keep the Aimpoint at the proper height.

KAC RAS II Production Model

Quarterbore's Note: Dave Lutz, V.P. of "Military Operations and Support" at Knight’s Armament Co was generous enough to provide the information posted on this page. I wish to thank Dave for providing these details about this exciting new RAS system!

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This site was last updated 01/10/04