As mentioned in a a previous post Brownells has been lstening to what shooters want and they have been adding 308 AR parts almost if not weekly. The latest edition is the JP LOW MASS BOLT CARRIER GROUP JPBC-4BA for 308 AR
JP defies current heavy is better logic of both the AR-15 and AR-308 platforms with the Low Mass Bolt Carriers and in the case of the AR-15 Low Mass Buffer.
I have not seen any analytical data on what system is best in the 308 AR and therefor have no opinion other than JP RIFLES knows the 308 and they have been doing it longer than most. Their rifles constantly win competitions.
I plan on contacting JP for a better explanation.
JP LOW MASS BOLT CARRIER GROUP for 308 AR - JPBC-4BA
Here’s what JP says about the LOW MASS system:
We have our own purpose designed operating systems. For the no-compromise competition rifle, the LMOS™ offers the most significant improvement in the felt impulse of the rifle as compared to any modification other than the addition of a compensator. The complete system consists of our low mass bolt carrier and lightweight buffer conversion kit. By reducing the reciprocating mass, the overall impulse as felt by the shooter is further reduced, and bolt velocity is increased without significantly affecting reliability. JP LMOS™ equipped rifles have virtually no reciprocating mass feel.
Reliability with these parts is excellent for competition use. We’ve been using this system for three years without a malfunction at a match. Most shooters that use and maintain this operating system feel that it is a great performance improvement. Some shooters have even reported fewer unexplained flyers in their groups with the JP LMOS™ system.
The JP Low Mass Carrier works out nicely in the new type of civilian machined receivers like ours and the DPMS High and Low Rider series that don’t have a forward assist. Although it doesn’t have the forward assist serrations, it functions in military type receivers. It just won’t allow the use of forward assist on the receiver. Dust cover functions normally.
You may be wondering why our stainless carriers appear black. This is due to a new state of the art surface finish for stainless called QPQ (Quench, Polish, Quench). This is a five-step process resulting in a rock hard surface with natural lubricity. Some want the bright polished look and that is available on the JPBC-3 Low Mass carrier, but not the JPBC-2 tactical carrier.
The JP LRP-07 has our large format AR-10 type Low Mass carrier. The JPBC-4 AR-10 low mass stainless bolt carrier is also finished in black QPQ hard coat for superior wear and natural lubricity. The JPBC-4 will also improve the sight recovery on the DPMS LR-308 or the Armalite AR10. However, it must be used with a DPMS LR-308 bolt assembly, firing pin, cam pin and firing pin retainer.
Do not attempt to use the JPBC-4 with the Armalite bolt assembly, firing pin or cam pin. Unlike the AR-15/M16 platform on which just about everything is cross compatible, each AR-10 type rifle such as the JP LRP-07, DPMS LR-308, Armalite AR-10, Knights SR-25 or Rock River AR-10 is inherently different with only limited cross compatibility of components. Always check compatibility anytime you order aftermarket accessories for AR-10 type rifles.