The handguard or forearm probably has the most options of any AR-15 component. You may decide your choice of hand guard is more important to you than the barrel length but keep in mind that that will also determine your gas system for the most part. Do you want a standard A2 (Colt) style handguard or a Magpul MOE handguard which gives you the traditional looking AR-15 upper or would prefer a free float style handguard where the handguard does not touch the barrel. Typically, a free float handguard and barrel combination will yield a more accurate rifle.

Free float handguards can be round aluminum tubes or open grid milled aluminum handguards. Quad rail handguards are popular for the various options you can mount to the many rails. Sites, optics, grips, lights, lasers are just a few options.

The barrel, handguard, barrel nut, gas block & gas system will need to be considered as a group in order to achieve your best functioning AR-15 complete upper.

The gas system is just the gas block (in front) and the gas tube that travels back to the inside of the upper receiver. The front gas block routes gas from a small hole in the barrel, through a tube to the upper receiver (and into the BCG) The gas block can have small rails on it or it may need to be a low profile so it can fit inside a free float handguard. Some gas systems work better with some barrel lengths and calibers so do your research.

Next Part 5 – The BCG