Final answer:
The buttstock assembly on the M249 automatic rifle supports all the major components, ensuring structural stability and providing comfort to the shooter when aiming and firing.
Step-by-step explanation:
In the M249 automatic rifle, the buttstock assembly serves as the support for all major components. It connects and supports features like the feed tray assembly, handguard assembly, and the gas regulator assembly, providing the necessary structure and stability. Being attached to the rear of the gun, it lets the shooter hold the firearm comfortably against their shoulder to absorb recoil while aiming and shooting.
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