Originally Posted by Villainous
I've settled with a Classic Army (if I could get my hands on one) M15A4 R.I.S Carbine (Rial Interface System) <-- I don't know if 'Rials' a spelling error, but it was made twice so it probably isn't, and if not, what does it mean?
That should be "Rail". A RIS is a system that replaces the standard forestock of the M4/M16 family of rifles with a set of Picatinny rail mounts for the attachment of accessories - light mounts, horizontal grips, laser painters, launchers, etc. Basically, it provides attachment flexibility to suit the operation at hand.