A question of rail systems

[Spartan198]

I was looking at the rail systems page of the KAC website (researching for a couple of custom AR carbine variants that I'm going to feature in a story) and they've got two different M4 rail systems shown. Does anyone here know the difference between the SOPMOD M4 carbine RIS and the M4 carbine RAS?

[Clutch]

Googling it found me this:

http://www.quarterbore.com/kac/kacrisras.html

If I'm reading the article right, the RIS system is a two-piece system, while the RAS is a single piece. The RIS also doesn't clamp on the barrel as tight as the RAS, allowing for different barrel profiles to be used in conjunction with it.

[jdun]

Both are two piece and both are overrated. For that amount KAC is asking I would expect it to be free floating. Both rails are drop in. In others worlds no gun smiting are necessary.

http://www.bravocompanyusa.com/Tactical-Handguards-Non-Free-Float-s/53.htm