Anyone know what optics system it was designed for?

Well a Aimpoint in a ARMS mount on top of the hump cowitnesses perfectly...

Quoted: Anyone know what optics system it was designed for?

The KAC RASII and Aimpoint have a perfect marriage

Old outdated pic of mine but it shows the main idea

Quoted: Quoted: perfect marriage

Nice setup, even it is old.  Couldn't get past the oxymoron you used to describe it, though.

kewl, that's what I needed to know. Thanks.

View from the right side...

Curious to see if your RAS II fits like mine does. I just bought it recently and after installing it as per Knights instructions I noticed that it has a little bit of play to it. Is this inherent in the free floating handguards or is it particular to the RAS II. I have a CQD vertical grip installed and when I rock the grip back and forth I feel the RAS shift in the front where the bottom handguard inserts into the top handguard. I can do the same thing by just grabbing the two handguards all the way to the front and squeezing them together with my fingers. Just a very little amount of play but I wondered if it was normal. Thanks.

With the RAS II there is plenty of room for a ACOG also if you wanted to go that way.  

Quoted: Curious to see if your RAS II fits like mine does. I just bought it recently and after installing it as per Knights instructions I noticed that it has a little bit of play to it. Is this inherent in the free floating handguards or is it particular to the RAS II. I have a CQD vertical grip installed and when I rock the grip back and forth I feel the RAS shift in the front where the bottom handguard inserts into the top handguard. I can do the same thing by just grabbing the two handguards all the way to the front and squeezing them together with my fingers. Just a very little amount of play but I wondered if it was normal. Thanks.

That is normal for the area you described.  For the benifit of those who don't have a RAS II in front of them to refrence, this is the area toward the muzzle, where the lower handguard is retained by hooking (more or less) into cutouts in the upper handguard section.  The rear of the lower guard can either be retained by the force of the delta ring (like regular HGs for quick removal & swap to an M203), or secured by the clamp to the barrel nut.

This lower section will have some play in it because regardless of the rear clamped area, the front is only hooked in.  The one-piece top handguard should be absolutely rigid, as it comprises both the top rail (for optics/lasers) and the side rail. (lasers/lights)

I noticed this too the first time i took mine out, but not to worry, this lower section does not have to be absolutely rigid unless your using a laser mounted on the bottom rail.

Tex78  

double post

So does the "hump" in the RASII take the place of the spacer when mounting an Aimpoint for it to cowitness?  I'm looking at getting a KAC rail system and I'm running the ARMS cantilever extension for my optic on my flattop.  Would I be better off going with the M4 Carbine RAS (KAC #98064)?

Quoted: So does the "hump" in the RASII take the place of the spacer when mounting an Aimpoint for it to cowitness?

Yes.

ACOGs, Aimpoints, and EOThingies will all work.