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General | Aluminum LMOS | Steel LMOS | FAQ

JP Low Mass Operating System


For the no-compromise competition rifle, our Low Mass Operating System (LMOS™) offers the most significant improvement in the felt impulse of the rifle compared to any modification other than the addition of a compensator. By reducing the reciprocating mass within the operating system, the bolt velocity is increased while simultaneously reducing the overall impulse experienced by the shooter with each shot. Consequently, LMOS™ equipped rifles have virtually no reciprocating mass feel and move less during cycling, allowing for much faster sight recovery and follow-up shots.

While use of the LMOS™ components is recommended only for competition and sporting use, this is only precautionary as their reliability is excellent, particularly on rifles with adjustable gas systems. Like all our bolt carrier designs, LMOS™ carriers feature a 100% increase in bearing surface for smoother operation, improved alignment and lower wear in the upper receiver as well as the longer Mil-spec. cocking pad for optimal reliability. In fact, Team JP shooters have been using the LMOS™ system for over a decade without any reported operating system malfunctions at a match, and most every shooter that implements this operating system feel that it is proven to be a great performance improvement. Some shooters have even reported fewer unexplained flyers in their groups after switching to the LMOS™ system.

For small-frame rifles, the complete JP LMOS™ system consists of one of our low mass bolt carriers and our lightweight buffer conversion kit, but any LMOS™ component can be installed individually in your existing setup and run smoothly. Click on the tabs above to see more about the different LMOS™ carrier models we offer.


Low Mass Operating System | Aluminum
JPBC-1JP Ultra LMOS™ Bolt Carrier
   Small-Frame
   7075 T6 Aluminum
   Anodized
$339.95
JPBC-1AJP Ultra LMOS™ Carrier Group with JP EnhancedBolt
   Small-Frame
   7075 T6 Aluminum
   Anodized
$460.95
Low Mass Operating System | Steel | Small Frame
JPBC-3JP LMOS™ Bolt Carrier
   Small-Frame (.223)
   Stainless Steel
   QPQ Black Finish
$225.95
JPBC-3SPJP LMOS™ Bolt Carrier
   Small-Frame (.223)
   Stainless Steel
   Polished Finish
$225.95
JPBC-3AJP LMOS™ Carrier Group with JP EnhancedBolt
   Small-Frame (.223)
   Stainless Steel
   QPQ Black Finish
$352.95
JPBC-3SPAJP LMOS™ Carrier Group with JP EnhancedBolt
   Small-Frame (.223)
   Stainless Steel
   Stainless Finish
$352.95
JPBC-3A-6.5GJP LMOS™ Carrier Group with 6.5G JP EnhancedBolt
   Small-Frame (6.5 Grendel)
   Stainless Steel
   QPQ Black Finish
$366.95
JPBC-3SPA-6.5GJP LMOS™ Carrier Group with 6.5G JP EnhancedBolt
   Small-Frame (6.5 Grendel)
   Stainless Steel
   Stainless Finish
$366.95
Low Mass Operating System | Steel | Large Frame
JPBC-4JP LMOS™ Bolt Carrier
   Large-Frame (.308)
   Stainless Steel
   QPQ Black Finish
$269.95
JPBC-4SPJP LMOS™ Bolt Carrier
   Large-Frame (.308)
   Stainless Steel
   Polished Finish
$269.95
JPBC-4AJP LMOS™ Carrier Group with JP EnhancedBolt
   Large-Frame (.308)
   Stainless Steel
   QPQ Black Finish
$445.95
JPBC-4SPAJP LMOS™ Carrier Group with JP EnhancedBolt
   Large-Frame (.308)
   Stainless Steel
   Polished Finish
$445.95
JPBC-4AHPJP LMOS™ Carrier Group with High Pressure
JP EnhancedBolt

   Large-Frame (.308)
   Stainless Steel
   QPQ Black Finish
$470.95
JPBC-4SPAHPJP LMOS™ Carrier Group with High Pressure
JP EnhancedBolt

   Large-Frame (.308)
   Polished Stainless
   QPQ Black Finish
$470.95

Aluminum Ultra Low Mass Bolt Carrier


While we introduced the original aluminum bolt carrier over a decade ago, we finally discontinued it after several customers had difficulties with its rather strict maintenance needs and changed over to our stainless steel design. As it turns out, we left a gaping hole in the market with some devoted customers hoarding the old parts or buying them up at steep prices. To meet all that pent-up demand, we've gladly reintroduced a new-and-improved and easier to run ultra low mass carrier manufactured from aircraft-grade 7075-T6, the reborn JPBC-1.

Reengineered for improved reliability and performance with lower maintenance requirements, the new JPBC-1 is the ultimate in improved reliability and performance, especially when combined with a high-efficiency JP muzzle brake, adjustable gas system and Silent Captured Spring. The end result is a carrier that leaves your .223 shooting like a rimfire .22.

The JPBC-1 checks in at 2.9 ounces less than our 416 LMOS™ carrier and 0.7 ounces less than even the titanium carriers offered on the market today. Each unit comes as a complete kit including our JP precision-ground, one-piece gas ring as well as a titanium firing pin. Run in concert, this gas ring ensures perfect bore-to-gas seal fitment in the JPBC-1 and minimized friction to enhance reliability when fouled while the titanium firing pin eliminates any possibility of slamfire at the higher bolt velocities.

Once you've tried the new JPBC-1, like us, you'll wonder how we could have abandoned the concept in the first place.


Low Mass Operating System | Aluminum
JPBC-1JP Ultra LMOS™ Bolt Carrier
   Small-Frame
   7075 T6 Aluminum
   Anodized
$339.95
JPBC-1AJP Ultra LMOS™ Carrier Group with JP EnhancedBolt
   Small-Frame
   7075 T6 Aluminum
   Anodized
$460.95

Steel Low Mass Bolt Carriers


With all the durability and longevity of a Mil-spec carrier but lighter by 2 oz., our stainless steel LMOS™ carriers are a perfect for any of the wide range of civilian machined receivers on the market. The reduced profile of the these carriers removes material to reduce weight but sacrifices none of the critical operating dimensions save for the forward assist serrations. Even then, these LMOS™ carriers still function equally well in military-style receivers with the exception of the forward, which already sees sparse competition or sporting use. The dust cover feature of such receivers is unaffected.

Beyond their design features, our stainless LMOS™ carriers come in one of two finish options. The stainless models undergo a vigorous polishing process to bring out the maximum of the steel's natural luster for an eye-catching component that wouldn't look out of place in a jeweler's cabinet. Alternately, our black models undergo a state-of-the-art, multi-vendor process known as QPQ (Quench-Polish-Quench) that results in a durable rock-hard surface with remarkable natural lubricity and sheen.

To meet all needs, each of these models is available as a carrier alone, a complete bolt group, or a home builder bundle in combination with various billet receivers.


Low Mass Operating System | Steel | Small Frame
JPBC-3JP LMOS™ Bolt Carrier
   Small-Frame (.223)
   Stainless Steel
   QPQ Black Finish
$225.95
JPBC-3SPJP LMOS™ Bolt Carrier
   Small-Frame (.223)
   Stainless Steel
   Polished Finish
$225.95
JPBC-3AJP LMOS™ Carrier Group with JP EnhancedBolt
   Small-Frame (.223)
   Stainless Steel
   QPQ Black Finish
$352.95
JPBC-3SPAJP LMOS™ Carrier Group with JP EnhancedBolt
   Small-Frame (.223)
   Stainless Steel
   Stainless Finish
$352.95
JPBC-3A-6.5GJP LMOS™ Carrier Group with 6.5G JP EnhancedBolt
   Small-Frame (6.5 Grendel)
   Stainless Steel
   QPQ Black Finish
$366.95
JPBC-3SPA-6.5GJP LMOS™ Carrier Group with 6.5G JP EnhancedBolt
   Small-Frame (6.5 Grendel)
   Stainless Steel
   Stainless Finish
$366.95
Low Mass Operating System | Steel | Large Frame
JPBC-4JP LMOS™ Bolt Carrier
   Large-Frame (.308)
   Stainless Steel
   QPQ Black Finish
$269.95
JPBC-4SPJP LMOS™ Bolt Carrier
   Large-Frame (.308)
   Stainless Steel
   Polished Finish
$269.95
JPBC-4AJP LMOS™ Carrier Group with JP EnhancedBolt
   Large-Frame (.308)
   Stainless Steel
   QPQ Black Finish
$445.95
JPBC-4SPAJP LMOS™ Carrier Group with JP EnhancedBolt
   Large-Frame (.308)
   Stainless Steel
   Polished Finish
$445.95
JPBC-4AHPJP LMOS™ Carrier Group with High Pressure
JP EnhancedBolt

   Large-Frame (.308)
   Stainless Steel
   QPQ Black Finish
$470.95
JPBC-4SPAHPJP LMOS™ Carrier Group with High Pressure
JP EnhancedBolt

   Large-Frame (.308)
   Polished Stainless
   QPQ Black Finish
$470.95

FAQ

What parts do I need for the Low Mass Operating System?

Our low mass bolt carriers do not require that you also use our LMOS buffer (JPLMB) to function, and a low mass buffer can be used with a full mass carrier. Both reduce the mass of the reciprocating parts in the rifle, and the effects are essentially accumulative. Each one has some effect by itself while using both has more effect.

Both a low mass carrier and buffer are drop-in parts for a standard AR, i.e., neither part typically requires an adjustable gas system or any other special parts to function. The JPSCS is also a low mass part and is actually lighter than the LMOS buffer.

The gas system setting adjustments required for changing between LMOS and FMOS are so small that many people never bother to make any adjustments when switching carriers between rifles. If you are running the gas system at the absolute minimum setting for a particular load with no margin for error, then you may have to readjust your gas system. Otherwise, you should be able to just swap the carrier.

Why is my aluminum carrier (JPBC-1) showing wear?

The JPBC-1 is aluminum with hardcoat anodizing, which wears faster than the QPQ coating of our steel carriers. Because of this, it will not take long for you to notice cosmetic impact wear in the anodizing on both the front corners and cocking pad of the carrier. This is normal break-in wear. It does not indicate any current or future functional damage and is not a cause for concern.

The cocking pad wear can be minimized by using a JP Speed Hammer or other hammer with a radiused leading edge. Hammers with a sharp corner, such as a Mil-spec hammer, will create the most wear on the cocking pad of the carrier.