We source these buffers from CMMG.
Weight and composition of carbine buffers:
H1: 3.7oz, contains 1 tungsten weight + 2 steel weights
H2: 4.6oz, contains 2 tungsten weights +1 steel weights
H3: 5.4oz, contains 3 tungsten weights
M4 Carbine is equipped with the H1 buffer, though most 14.5" rifles would benefit from the H2 buffer found in M4A1. AR15s with barrels shorter than 14.5” will need some testing with H2 or H3 buffer combinations to proof out which is most reliable.