With all of the rails systems currently available there seems to be a product to fit most individuals budgets and needs.  I have a question about the FF RAS and the M4  RAS that I hope some other end users may help me with.  Currently I own a ARMS #45 and have a RAS-II in route.  I do not own any optics (this will change), but I do use a Surefire M962SU06 and a AAC vertical grip which are both mounted to the ARMS #45.   Both the AAC grip and the Surefire can be readily placed on both the #45 and the RAS-II.

Now the question.  Several of my old uppers are A2s which are not compatible with the RAS-II or ARMS #45.  I like the ideal of being able to add my flash light and vertical grip to these uppers as well.  It is my understanding that the M4 RAS fits in the delta ring like normal hand guards and only requires two set screws to be tightened?  This would fit my needs but since the FF RAS is only $20 more I want to know what is involved with it's installation?  Another concern of mine is over rumors that state the FF RAS under full auto or rapid fire could potentially warp the receiver while a vertical grip was in use.  Is there any substance to this statement?  

In the end what all of this amounts to is myself trying to avoid buying more that one weapons light such as the M962SU06.  I would like to be able to switch my weapons lights, vertical grips and other rail mounted accessories between all of my carbine upper, both A2 and A4, with minimal trouble. Thanks for all future responses.  And, yes I do own a Colt M16 model 614.

The Azalin

I have done some pretty harsh testing to determine cook-off rates for M4's equipped with both the FF RAS and the standard M4 RAS with vertical grips. I have never experienced any sort of catastrophic failure with either... This has been posted (read: perpetuated) on the boards here, but we at KAC have never received an official statement, report, or document from the government or other entity outlining this "engineering defect".

The main difference between the two systems are that the Free-Floating RAS requires removal of the flash-hider, front sight tower, and barrel nut for installation. It also enhances accuracy, by virtue of free-floating the barrel.

Clint Lynch
Product Design Engineer
Knight's Armament Co.

(Finally beat Lutz to a post...)

If I'm interppreting your question correctly, your asking if you can put the KAC [s]RAS II[/s][noclue] FF RAS on an A2 upper, as the ARMS #45 obviously will not. The Answer is yes, following the procedure posted by Troy.

- and Thanks to Havoc for posting! [beer]

I believe notack meant the FF RAS, not RAS II.  RAS II will not fit an A2 upper...only flattops.

Let me get this straight.  The difference between RAS and FF RAS is that the FF RAS in more accurate (to what extent?) and it is more difficult to mount on the M4?  Where can you get prices on them.  I've seen plenty of pics but no prices.

TS

Since our (KAC) FF RAS allows the host weapon barrel to "free-float", there is accuracy enhancing potential there, especially with match grade ammo.
Our M4 Carbine RAS and M5 Rifle RAS "touch" the host weapon barrel in the same way as issue plastic handguards.  So these are not classified as FF.
There is only one screw at the rear of the M4 or M5 RAS; at the rear, where it forms the top of a "triangle", and when its tightened, aligns the RAS to the barrel nut. The two lower points of the triangle are two oposing dowel pins that index to the barrel nut's 10 and 2 o'clock gas tube slots.  This is a patented and very secure (i.e., accuracy) assembly.
At the front of each RAS, there is a spring loaded spacer that minimizes the "warp" or walking effect of a hot barrel "moving the rail" out of its normal "cold" alignment to the sights.  However, this is a very small deflection and hardly measureable with GI ammo.
ColdBlue sends...

Thanks Cold Blue,

Just trying to decide if I need a regular or FF RAS.  Mine would have an EOTech partially mounted on it.  That is mounted on both the flattop and the RAS and I would have a foregrip.  Thanks,

TS

Many of the vendors here on AR15.com sell the RAS systems.  Check the EE.  

Thanks Calvert,

TS

I know that neither the RAS-II or the ARMS #45 will fit an A2 upper.  My question was related to the FF RAS and M4 RAS.  I know both models will work with an A2 upper.  My question centered around ease of installation, and were there any legitament concerns related to warping the upper receiver during full auto use, while using the FF RAS.  According to Havoc there is no validity to the upper warping issue, so I will trust in his experience.  Since the M4 RAS is almost as simple as installing normal handguards I will probally buy it.  I like the advantages of being able to swap the M4 RAS quickly between uppers with out having to dis-assemble the entire upper.

The Azalin

DOH!!! [s] RAS II[/s], FF RAS [:I]

The FF RAS less expensive?

[<|:d>]

Labor difference if you do it?

TS

You'll probably be getting some business from me.  Not soon, but not a long time either.

TS

Will the EOTech mount on the top rail and across to the FF RAS at the same time?  I know that on the regualr RAS you can slide a rail panel on the top rail by going over the main rail and inserting it from behind but the barrel nut cover/cap of the FF RAS wont allow this.  Does this prevent mounting an EOTech across the nut cover/cap?

i'm pretty sure it won't fit.  my buddy was over the other day to pick up his eotech 551 from me and brought along his upper with FF RAS MRE, and we were playing around with it.  looked like you either mount it on the flat top, or on the rail, but not across both.  i think you're right, the nut/cover gets in the way.
cheers,
MM

You can either mount it on the receiver or the RAS, but since the 552 is much longer, it will cross the both platform.

[img]http://www.thermaldynamics.com/pictures/guns/M4MRE-1.jpg[/img]

SMG,
will only the battery housing cross both rails, or will the mounting clamp ALSO cross both rails?  nice floor :-P
thanks,
MM

EagleFirearms (check EE) has the FFRAS for $300.

MM,

The cross bolt sits on the second rail on the receiver and the battery compartment crosses the locking nut of the FF RAS.

You are welcome to come over the house the enjoy the floor anytime. :)

So if you mount an EOTech 552 with the screw in the second slot from the "gap" of the flattop will it work?  Is some of this in your article on the Marlyland AR15 Shooter Association?

Thanks,

TS

ok, got confirmation that the clamp portion of a 551 (same as the 552) will NOT straddle the barrel nut/cover of the FF RAS.
cheers,
MM

Tiger,

This wasn't covered on Maryland article, but no stress in applied to barrel nut on he RAS because the EOTech doesn't really touch it.

Cool, Chen.  



Thanks,
TS