What component houses the action spring, buffer assembly, and extension assembly?

The component that houses the action spring, buffer assembly, and extension assembly is the buttstock. The buttstock is crucial in the operation of the rifle as it provides a stable platform for the user to shoulder the weapon while also providing essential components for the weapon's cycling and recoil management.

Inside the buttstock, the action spring and buffer assembly play significant roles in mitigating recoil and cycling the action during firing. The buffer assembly absorbs the rearward movement of the bolt carrier group and aids its return to battery for the next round. The extension assembly, also found within the buttstock, is designed to connect the buttstock securely to the receiver, providing structural integrity and allowing for proper alignment of the action components.

Understanding this configuration is important for maintenance and troubleshooting, as any issues with the bolt carrier cycling or felt recoil may often be traced back to components housed within the buttstock. The other components listed, such as the receiver assembly, gas block, and barrel assembly, play vital roles in the overall function of the rifle but do not contain these specific internal parts.