Colt H-Series buffers are an excellent reliability upgrade shooters can make to their AR-15 carbines. Heavy buffers can reduce felt recoil as well as reduce the cyclic rate on full-auto rifles. Standard carbine buffers contain three steel weights, the H buffer has two steel weights and one made from heavier tungsten. The H2 has two tungsten weights and one steel, and the H3 has all three weights made from tungsten. 

Caution must be used when adding weight, as too heavy of a buffer can inhibit reliable function. As a rule, shorter gas systems benefit the most from heavier buffers. 

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