Hi Hurry1996...If you're looking for a drop-in, no modifications replacement for the standard hand guards, I just purchased a Monstrum Tactical AR-15 Quad Rail Handguard, Carbine Length, Drop-In, Black - the MSRP is $34.95, the regular price is $19.95 (what I paid), and right now, it is on sale for $12.95! It is really well machined, uses 4 allen screws with wrench included, and from the website, "aircraft grade aluminum, both sturdy and lightweight, it weighs in at a mere 12 ounces. It is 6.7 inches in length, 2.5 inches in height, and 2.5 inches in width. The internal diameter is 1.7 inches at its narrowest." And on our AR-556, with the Ruger Delta Ring, installation is a snap - maybe 10 minutes tops. Here's the link to their website - http://monstrumtactical.com/collect...ail-carbine-drop-in-black?variant=15621183235
Be sure to read the reviews - there is one from another AR-556 owner, and he says, "I bought this for my Ruger AR-556, it fit perfect. The quality of the rail seems very good. And for the price you can't go wrong."
I looked at a lot of options on the web and in stores, and never found one that I liked better for this good a price (even on eBay). Hope this helps and good luck.