JP Enterprises VMOS Variable Mass Heavy Bolt Carrier LR-308 Stainless Steel QPQ

  • Product #: 304259
  • Manufacturer #: JPBC-7H2
  • UPC #: 812872024226
JP Enterprises VMOS Variable Mass Heavy Bolt Carrier LR-308 Stainless Steel QPQ
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Product Overview

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 our Silent Captured Spring, multiple masses are exchangeable to perfectly tune your operating system weight. This heavy version of the large-frame VMOS carrier includes one steel and two tungsten weights, which can be exchanged for lighter steel weights. Package includes carrier, Enhanced Gas Ring and instruction sheet. Requires DPMS-pattern bolt, firing pin and cam pin. Works best with 284263.



The large-frame VMOS™ carrier uses the same steel and tungsten weights as GEN 2 Silent Captured Spring units. Only the forward two masses are reconfigurable. The rear-most steel mass cannot be exchanged.

This carrier will not cycle with a standard buffer retainer plunger installed. Standard buffer/spring components must be installed “loose” or replaced with a Silent Captured Spring.

This notice pertains to any rifle based on the large-format AR-10-type or LR-308 platform typically chambered in .308 Winchester, 7.62x51 NATO or other cartridges requiring the longer magazine format.

Be aware that these receiver platforms are not standardized like the AR-15/M16 platform for which most parts are cross-compatible. Before ordering accessories and parts for your large-format rifle, make sure the parts are compatible with your particular platform. This bolt carrier is compatible only with the DPMS family of AR-10 products.

With the Armalite/Rock River family of large-frame receivers, this carrier can only be used as a complete bolt carrier assembly group with a DPMS-pattern bolt such as our .308 JP EnhancedBolt. Interchanging individual components will result in an unsafe configuration. Do Not under any circumstances mix and match components between the platforms.



  • Enhanced tunability of operating system
  • Guaranteed reliability of difficult configurations
  • Overcomes all fouling build-up
  • Roller-burnished bore for frictionless operation
  • Rock-hard QPQ finish provides remarkable natural lubricity
  • Extremely smooth cycling with proper lubrication
  • Increased bearing surfaces for slower wear and longer component life
  • Longer cocking pad for optimal reliability
  • Additional forward assist serrations for one full inch of travel
  • American made

Additional Information
WARNING: Cancer and Reproductive Harm -


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NOTE: Prices, specifications and availability are subject to change without notice. We reserve the right to correct typographic, photographic and/or descriptive errors.