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by RMIII, from FL, United States Asked on November 30, 2022
The Primary Weapons Systems MK218 MOD1-M 18in bbl Upper Receiver .308 Match can fire 7.62x51 ammo but is recommended to use .308 Win ammo. I recommend contacting Primary Weapons Systems in regard to their recommendation of using 7.62x51 ammo with this upper and if it impacts the warranty.