I'm trying to find info on this. But really cannot find any detailed info. I know RIS stands for Rail Interface System. But what is RAS and what's the difference? Does anyone have opinions or preferences?

Royal Air Service. It was originally designed for the British air forces for use in attaching a Heads Up Display sight, so Harrier pilots can engage enemy aircraft in an emergency. You know, when the 25MM runs out.

OHH that helps a lot thanks!
[BD]

And while we are at it... Why do people say you can use a M4 RAS ONLY on a M-4 profile barrel while the RIS for the carbine can work with any upper?

Also, if the statements that I keep reading that the M4 RAS will not work with an HBAR... Why does the M5 RAS work with an HBAR?

.........................................

Some answers that I know...

The RIS and RAS both function the same the difference is in the way they mount.  The RAS is tighter fitting than the RIS and the RAS uses a special Clamp assembly that helps attach the RAS to the barrel nut and forend cap.

I have the M5 RAS and I had it mounted on my AR-15 and now it is mounted on my AR-10.  I have never handled an M4 RAS or RIS.  I also have a M4 FF RAS which is an entirely different beast...

I am selling my FF RAS... [url]http://www.ar15.com/forums/topic.html?id=74139[/url]

Rail Adapter System.

[(:)]

[url]http://www.impactguns.com/store/kmc_mws.html[/url]

[url]http://www.jtdistributing.com/ar15/knights_armament.shtml[/url]

Here´s the KAC M4 RAS(PN 98064) on my carbine. It is extremely solid, even when i mounted it and hadn´t tightened the clamp on the rear part, it was VERY solid.

100% good to go.

[img]http://wsphotofews.excite.com/024/Gk/Jh/7E/9189862.jpg[/img]

Here´s a closer shot from the left hand side.

[img]http://wsphotofews.excite.com/026/EO/Lw/xn/VB47892.jpg[/img]

I`ve got a new Bushmaster Dissipator in transit to me now, should be able to pick it up next Wednesday. I`m thinking about M5 RAS/RIS, or  whatever it is and trying to gather info on it. So I can make a educated decision. Thanks for any help. Wish I could get free float style but that looks like a no go.
[}:)]

Then I assume you have seen this thread...

[url]http://www.ar15.com/forums/topic.html?id=69780[/url]

It looks like you will need to modify the gas block which will be under the RAS but otherwise the M5 RAS (according the the above thread and pictures) will work!

Here is a helpful PDF file....

[url]http://www.biggerhammer.net/patents/us05826363__.pdf[/url]

Here is a good thread...

[url]http://www.ar15.com/forums/topic.html?id=70032[/url]