When I first launched 308AR.com my first email seeking information on the DPMS LR-308 style rifles was to JP Rifles. Imagine my surprise when I received a very detailed response from John Paul Gangl himself. John Paul is JP and make no mistake he understands this platform more than most. I will be forever grateful for that first contact.
JP Rifles AR-10 Compatibility
(as published in the 2011 Price List) Visit JP Rifles
This notice pertains to any rifle based on the large format AR-10-type or LR-308 platform typically chambered in .308 Winchester, 7.62×51 NATO or other cartridges requiring the longer magazine format. This includes, but is not limited to, the ArmaLite AR-10, Bushmaster BAR-10, Rock River LAR-8, DPMS LR-308, KA SR-25/M110 series, POF P-308 series, Larue Tactical OSR and JP LRP-07™.
Unlike the AR-15/M16 platform, for which most parts are cross compatible due to the receivers’ standardized design, the large format platforms have not been standardized. Before ordering accessories and parts for your large format rifle, make sure the parts are compatible with your particular rifle platform. The only parts that are universally cross compatible are fire control components. Hand guards and barrels are each slightly different and may not be cross compatible.
Hand Guards: In the JP nomenclature for hand guards, the “D” at the end of the part code refers to rifles using the DPMS LR-308 thread pattern on the upper receiver barrel collar. The “A” refers to rifles using the Armalite thread pattern, which includes the Bushmaster BAR-10 or Rock River LAR-8. JP hand guards using the letter “M” are only compatible with the AR-15/M16 platform and will not fit on any AR-10-type rifle.
Barrels: JP Supermatch™ barrels in .308 Winchester/ 7.62×51 or .260 Remington are compatible with most AR-10 platforms except the Rock River LAR-8 or Bushmaster BAR-10. Due to the use of an FAL magazine, the extension piece on the barrels used in those rifles must be extensively modified to allow for feeding. Therefore, JP .308 and .260 barrels are not compatible with the RRA or BM rifles. However, our barrels may be modified to work with the LAR-8 or Bushmaster BAR-10 rifles.
Gas Tubes: The gas tubes used in the ArmaLite rifles is longer than the gas tubes used in all other platforms. Standard gas tubes are not compatible with ArmaLite rifles or in particular, barrels using the ArmaLite port position.
Fire Control Parts: All the large format variants that we are aware of will accept standard AR-15 type fire control components, but the setup may vary significantly between platforms. In the case of JP Fire Control Components, it is essential to use the “red” hammer spring provided with the kit. The hammer spring must be of a higher spring rate to ensure both ignition reliability and resistance to finger bounce-off doubling. Release weight on a .308 caliber self-loaders must be at least 3.5 lbs. or greater. With a lighter release than this, you may experience finger-bounce doubling or the firing of more than one round with each pull of the trigger. This is not acceptable for both safety and legal reasons.