Exoskeleton # 2

AR Upper Receivers

Continuing the exoskeleton theme from last week, an AR upper receiver is the exoskeleton for the bolt carrier group and the barrel.

Functionality

The upper receiver provides a channel for the bolt carrier group to ride in as it goes back and forth. The upper receiver provides a secure attachment point for the barrel. There is an opening in the upper receiver for the gas tube. It has a slot for the charging handle. The upper has a port for the spent cartridge to egress the rifle as it is extracted from the chamber after firing. That port has a dust cover for when the weapon is in storage. There is a “forward assist” on the upper receiver to nudge the bolt into battery if necessary. The upper has an attachment mechanism for the handguard that surrounds the barrel. The upper has tabs on the bottom with holes for pins that are used to attach it to a lower receiver. The pins are part of the lower receiver. Finally, the upper on the majority of modern AR-15’s has a Picatinny rail on top for attaching accessories. The rail is most often used for attaching sights and optics. You can still buy a “carrying handle” upper. More on that below.