Building an AR-308 from an 80% Lower thumbnail image

Building an AR-308 from an 80% Lower

5D Tactical - 4th Nov 2016

AR-308 (LR-308, .308) lower receivers are a bit more complicated than AR-15 lower receivers when it comes to puzzle-piece building a rifle, as one would be required to do when finishing an 80% lower receiver. The AR-15 is extremely modular, one of the factors that contributes to its immense popularity, and typically parts sourced from various manufactures will fit together without any trouble. This is not necessarily the case with the AR-308 platform. Allow us to explain.

As none of the major AR-308 manufacturers offer 80% lower receivers, it’s up to those of us in the 80% lower industry to develop products based on established compatibility controls. This is mainly due to the fact that we want to make it as simple as possible for our customers to build their freedom machines with as little trouble as possible. The aim of this article is to educate our existing and potential customers on questions pertaining to platforms and compatibility as they relate to our AR-308 80% Lower Receiver products.

There are two major platform types for .308 semi-automatic rifles. They are referred to as AR-10 and LR-308 (commonly AR-308). A brief history lesson will show that the AR-10 platform was developed by the Armalite company and first released in the 1950s. For the sake of better understanding, think of Armalite’s AR-10 platform as the Betamax or HD DVD of the .308 world. They were first, but their platform is not as standardized or prominent in the market today. On the other hand, the “DPMS platform”, or LR-308 (AR-308) could be considered the VHS or Blu-ray of the .308 world. DPMS brought the semi-automatic .308 rifle to prominence with their Panther LR-308. Okay, maybe this isn’t the best analogy since unlike the Betamax and HD DVD, the AR-10 is still sold today, but hopefully the point isn’t lost.

As of today, the DPMS platform is more common, and the components offered are more modular as compared to the AR-10. AR-10 parts are harder to come by, and they are not as interchangeable between manufacturers. Because of these reasons and others, the AR-10 platform would not be ideal for 80% lower receivers. Many AR-308 component types are referred to as “DPMS compatible”. Our 5D Tactical AR-308 80% Lower Receivers are what would be considered DPMS compatible. What this means is important when it comes time to purchase upper receivers, lower parts kits, etc.

To add further confusion, DPMS recently released a smaller version of their LR-308, now what some refer to as “DPMS Gen 2”. The DMPS Gen 2 is more dimensionally similar to an AR-15, and this is not what we would recommend you look for when building up one of our AR-308 lower receivers. AR-308 parts and components labeled DPMS Gen 1 are what our lower was designed around and thus they will be most likely to fit our lower receiver, with or without slight modification.

Our lower receiver is designed to work with components from DPMS, CMMG, Aero Precision and other smaller companies who market their .308 components as DPMS compatible. Upper receivers, lower parts kits, and other parts should drop right on and work out of the box. Occasionally, minor modifications will be necessary when building an AR-308. This is not limited to our lower receiver, it’s the nature of all AR-308 builds. For example, in testing we found some Aero Precision upper receivers may need the rear takedown lug drilled to a slightly larger size as it is slightly different from the DPMS and CMMG uppers. Some companies like PSA (Palmetto State Armory) will also work but you may need to file away a little material off the top of the buffer mount because their charging handle sits lower than everyone else’s.

Building an AR-308 is definitely more involved than making an AR-15 in regards to choosing components. When you get down to brass tacks, the simplest and easiest way to make an 80% 308 is to buy our Universal AR-308 80% Lower Router Jig, and buy our AR-308 80% Lower Receiver. Once you’ve quickly and easily transformed your AR-308 from paperweight status into a firearm using our jig, pick up an assembled upper receiver and lower parts kit from DPMS, CMMG or Aero Precision. Generally the buffer tube assembly and stock can be purchased anywhere with little worry of fitment issues. As with anything, a certain amount of research will be required by the end-user. When assembling an AR-308 for the first time, just keep the Dremel handy and you shouldn’t have any problems. We are hopeful that this tutorial will clear up a number of frequently asked questions. As always, please do not hesitate to contact us with any more questions.