Lets you skip all issues related to barrel nut clamp type handguards - Aero Precision M4E1 223 Remington/5.56 NATO Enhanced Upper Receiver

This upper receiver design was created to address long running issues with free float handguards that use the typical two bolt barrel clamp design.

The problem there is that most of those designs use a short proprietary barrel nut as the bearing surface for the clamping end of the handguard. In some designs that nut is also completely smooth and round. That leaves just the clamping force and perhaps some small aluminum tabs as the only things that prevent the handguard from rotating, flexing or even coming completely loose in the worst case. None of that is good.

The Aero design replaces that system altogether with a large, solid, fixed mount area that enhanced Aero handguards are bolted to by four sets of two screws spaced evenly around the entire front of the receiver. The possibility of rotation is completely eliminated, and the possibility of the handguard ever flexing or coming loose is reduced to near zero.

The downside is that you only get these benefits with Aero enhanced handguards that make use of the 8 screw attachment design. Other handguard designs can supposedly be installed with shims, but I don't see the point in not using this receiver as it was intended and getting the full benefit of the design.

Also, some people that like very slim handguards may not care for the diameter of the Aero enhanced guards. But I don't see the diameter as a drawback at all. It allows me to use almost any of the adjustable gas blocks under the guard, including my favorite by Superlative Arms.

On top of all of the design plusses, paired upper and lower receivers in the OD Green or Kodiak Brown anodizing look great and provide lots of options for builders who are tired of all black ARs.