I'd like to keep the rifle as light as possible and I guess I only really need a rail on the underside of the barrel for a foregrip since I won't really be putting an IR laser on the top rail or hanging anything off the sides or anything like that.

The older Bushmaster system was way lighter than their current setup.

They have both a tri-rail and single rail that mount to the bottom of the hand guard. Both are less than $20...<ul><li><a href="http://www.commandarms.com/">CAA...</a></li></ul>