For difficult setups like suppressed rifles and exotic caliber chamberings, some degree of mass regulation is required for optimal performance. This is especially true in the absence of an adjustable gas block. Residual gas and excessive fouling can grind your rifle to a stop. One size never fits all when it comes to gas-operated rifles. The Variable Mass Operating System (VMOS) carrier ensures reliability through additional reciprocating mass but provides more custom tunability. Combined with the Silent Captured Spring, multiple masses are exchangeable to perfectly tune your operating system weight. This standard version of the large-frame VMOS carrier includes three steel weights, two of which can be exchanged for heavier tungsten weights. Package includes carrier, JP Enhanced Gas Ring and instruction sheet. Requires DPMS-pattern bolt, firing pin and cam pin. Carrier works best with 284263.Notes:The large-frame VMOS carrier uses the same steel and tungsten weights as GEN 2 Silent ...