A .875″ gas block diameter refers to the size of the barrel journal where the gas block is installed, typically found on heavy-profile AR-15 and AR-10 barrels. This gas block size is designed to regulate gas flow for reliable cycling and is compatible with .875″ diameter barrels, gas tubes, and upper receiver components. It is often used in precision or competition builds, where a heavier barrel profile is preferred for accuracy and heat management.
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