I would like to know what the difference between the two.

Thanks,

Mike

The RIS (Rail INTERFACE SYSTEM) was designed as an after market accessory  to work on standard M4 carbine handguards. It takes  picatinny rails and bolts them on to the fat round handguards  of the M4. Then accessories, such as vertical foregrips, lights, scopes, etc can be slid on or  mounted on the rails. The RAS is an advancement in this technology where the whole front handguard set is replaced by two pieces with the rails molded in at the 12, 3, 6 and 9 o'clock positions. The lower part of the front end drops down for maintenance. I have a Stoner SR-15 M5, which uses this setup straight from the factory. A GOOD picture with descriptions of  the RIS this is at http://www.dynamicwave.freeserve.co.uk/arms/ M4accs.htm For a good pic of the RAS, try www.impactguns.com/store/kmc_ras_m16car.html  Protective panels attach at various points along the RAS to protect it and your hands. The RAS is made of very hard, durable polymer.  Hope this helps.

Not quite. The RIS (rail interface system) is nearly identical in construction, parts count, and installation as the RAS.
The RIS (rail interface system) came first, and is the system in use by the US Navy. It is secured to the fore-end by only one clamping foot, which clamps on the handguard cap at the front, and only fits certain diameter barrels.
The RAS (rail adapter system) is used by the US Army and Marine Corps. It has two clamping members, one at the barrel nut, and one at the handguard cap, providing a more secure platform for aiming-point critical accessories such as the PAQ-4C IR aimer and similar. It also fits a wider range of barrel diameters.
Both are machined from an aluminum extrusion, and have the same number of rails and cross-slots. There are RIS's and RAS's available for the carbine, however only an RAS exists for the rifle.

havoc is right.  The KAC webpage used to describe the difference.

Cool..good info. I described it as it was described to me. There are a bunch of pics at http://www.dynamicwave.freeserve.co.uk/arms/ which really show off a lot of the different variants.

[url]www.dynamicwave.freeserve.co.uk/arms/[/url]

[url]www.impactguns.com/store/kmc_ras_m16car.html[/url]