The JP Enterprises VMOS Large Frame Heavy bolt carrier (JP part no. JPBC-7H2) is a Variable Mass Operating System carrier for large-frame .308 rifles. JP built the VMOS to add reciprocating mass and mass tunability, which helps suppressed rifles and exotic chamberings that gas fouling and extra port pressure can push out of their operating window. This heavy version carries one steel and two tungsten weights that can be swapped for lighter steel ones. The carrier is stainless steel with a QPQ black finish, and this listing is the carrier alone.

Key Specifications

• The frame size is large frame (.308), made for AR-10-pattern rifles.
• The version is heavy, with a larger starting mass than JP’s standard VMOS carrier.
• The material is stainless steel with a QPQ black finish, which gives a hard, low-friction surface.
• The weights are one steel and two tungsten, and they can be exchanged for lighter steel weights to retune the mass.
• The bearing surface is increased by 100 percent, with a longer cocking pad for reliability.

Frequently Asked Questions

What does the VMOS carrier do? It adds reciprocating mass and lets you tune that mass, which helps rifles that run suppressed or in exotic chamberings stay inside their reliable operating window.

Does this listing include a bolt? No. This is the bolt carrier alone. JP sells a separate carrier group that adds its EnhancedBolt.

What weights does the heavy version include? It includes one steel and two tungsten weights, which can be exchanged for lighter steel weights.

Buy the JP Enterprises VMOS Large Frame Heavy Bolt Carrier, .308

For a suppressed .308 build, tuning mass at the carrier takes the guesswork out of reliability. Browse more parts in our other AR-15 accessories and parts section and order from our Lubbock, Texas gun shop for fast, insured shipping.