A question of rail systems
 

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?

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.

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/Tacti...Float-s/53.htm