The AR-308 and AR-10 are magazine fed, semi-automatic and modular rifles. Originally built by Eugene Stoner as a combat rifle, the semi-automatic .308 is a popular pick among gun enthusiasts looking for a rifle that’s suited for long range shooting and hunting. Although the rifle is less popular than the lighter AR-15 and was never adopted by the U.S. Military, the AR-308 still remains a great pick for custom build gunsmiths. Like an AR-15, you can also build your own AR-308 at home.
In fact, building an AR 10 .308 from an 80% lower receiver is easy. The rifle is chambered in the .308 caliber round and has more recoil than the .223 or 5.56MM typically used in an AR-15 due to its full powered round. Before diving into the details of how to build an AR-308, there are a few critical things that you should know.
The .308 Platform is Not Standardized
Unlike the AR-15 rifle which is pretty well standardized among various manufacturers, the .308 platform is not standardized. Take any two AR 15s and the chances are the majority of the parts can be interchanged. AR 10/.308s are different in that there is no standardization for construction of the rifle and different brands have different iterations of the .308 platform design. What does this mean?
In today’s market, you will find two main patterns of the .308 rifle: the Armalite pattern and the DPMS pattern. When selecting a AR-308 lower receiver for building an AR 10 .308, you must decide which type to choose for your custom home build. Both patterns can make a good rifle, but the DPMS comes with an advantage due to availability of parts, some of which are interchangeable with the AR-15. Most .308 80% lowers available on the market are manufactured to be compatible with the DPMS Gen 1 platform.
AR 10 .308 Internal Parts are Not Always Compatible
Because of the different AR 10 .308 rifle patterns, you’ll come across parts for both DPMS and Armalite, and upper receivers for each. Unfortunately, many of these parts are not interchangeable between AR 10 .308 rifles. Once you’ve decided what pattern lower to use for your custom build project at home, you’ll have to choose build parts that are compatible with your type of pattern lower. That includes the barrel and BCG.
DPMS pattern AR 10 .308 80% lower receivers do come with more options when you’re looking for parts needed to assemble your rifle. If you decide to build your AR-308 using an 80% lower receiver, you’ll also need a specific router jig for the custom build. Both the jig and lower must match to ensure an accurate build. When purchasing an 80% lower receiver for building an AR 10 .308, make sure to purchase a compatible 80% lower jig with the right tools. The 5D Tactical Router Jig PRO is a truly universal 80% lower jig, which is guaranteed to be compatible with all lower receiver styles, regardless of exterior dimensions.
AR 10 Lower Parts Kit
Due to the small difference between lower receivers, there are a few parts that are only compatible with AR10 lowers. These parts include the trigger, the trigger springs, and the safety, which can be easily swapped between the AR-10 .308 and the AR-15. Parts that are not compatible in any way include:
- Bolt catch
- Takedown pins
- Some pistol grips
- Magazine Catch
Buying AR 10 .308 Parts
Buying the right parts for your AR 10 .308 custom build is perhaps the most important step. With so many different types of .308 ARs out there, it can be hard to know which parts you need for the type of gun that you want to build. Not only do you need parts that fit, but also a gun that runs and functions reliably. The popularity of quality matched receivers from companies and 80% lower receivers as the platform of choice when it comes to building an AR 10 .308 rifle has gotten a lot of people interested in do-it-yourself AR-10 .308 rifle builds.
The problem is, without a basic understanding of how AR 10s work and the right parts for building an AR 10 .308, you could as well end up with an expensive but non-functional gun. If you have built an AR-15, you will agree that parts compatibility is one of the benefits of building one. However, this is not so with the AR 308. For home builders interested in learning how to build an AR 308, it means you can’t go ahead with purchasing parts without doing some research.
Here’s a complete list of .308 AR specific parts that you’ll need for your custom build:
- Upper and lower receiver
- Barrel of choice
- Handguard setup of choice
- Buffer and buffer spring
- Complete Bolt Carrier Group
- Ejection Port Door (unless you’re running a slick side upper)
- Takedown and pivot pins
- Muzzle device that’s threaded ⅝” x 24, for a .30 caliber
- Magazine catch/release
- Specific LPKs and triggers for the .308 ARs
Other parts you’ll need that also consist of AR-15 parts include:
- Pistol grip
- Complete lower parts kit
- Sighting systems, mounts, optics, backups/flips, red dots, etc
- Gas systems (Gas blocks and gas tubes).
Building an AR 10 .308 rifle at home is easy when you have all the right parts. It becomes even easier when you do your homework and know where to source all the components needed to complete your AR 10 .308 assembly.
Recommended Tools for Your AR-10 .308 Assembly
Most of the tools you’ll need for your AR 308 assembly as you learn and practice how to build an AR 308 are tools that you already have in your home garage or workshop. The recommended tools include:
- Armorer’s wonder wrench
- Lower receiver vise block
- Upper receiver vise block
- Small rubber mallet
- Bench vise
- Roll pin punch set
- Needle-nosed pliers
Assembling Your .308 Upper Receiver
If you’ve decided to assemble an AR 308 upper receiver from parts, you will have to follow a strict build procedure to ensure that everything works fine. The parts you’ll need include:
- DPMS AR 308 upper receiver
- Barrel nut
- Free float handguard
- Gas block
- .308 bolt carrier group
- Gas tube
- Charging Handle
Once you have all the parts ready, inspect each of them and do a test run to be sure that all the parts fit as expected. Follow these basic beginner steps while also referring to the provided assembly instructions that come with your upper receiver build kit.
- Prepare the AR 308 receiver by mounting it on your vise
- Install the barrel in the DPMS upper receiver
- Be sure to clean the barrel extension and the mating hole
- Apply grease to the threads and install the AR 308 barrel nut
- Tighten the barrel nut correctly while maintaining proper alignment with the gas tube, if applicable
- Install the AR 308 gas tube correctly (Actual installation will happen when the gas block is installed)
- Install the AR 308 gas block while checking the orientation of the holes in the gas tube
- Install the free float handguard, aligning the Picatinny rail with the rail of the upper receiver
- Install the AR 308 bolt carrier group and charging handle
Assembling Your .308 Lower Receiver
Building a DPMS AR 308 lower receiver from parts will also need some work and attention to small details. The average person with the proper tools and some mechanical skills can get the job done in about an hour or less. There are two ways to building an AR 10 .308 lower receiver: Purchase a lower parts kits specifically for the AR 308 or buy parts individually. Be sure to check if the kit has everything needed to complete the lower.
Some kits may not include a trigger and associated parts like the fire control group. Be sure to check that all the parts needed for the assembly are included and then follow these simplified steps to assemble your AR-308 lower receiver from parts.
- Install the AR 308 magazine catch into the recess on the left of the receiver
- Install the AR 308 bolt catch spring and then the buffer in the lower receiver
- Install the AR 308 front pivot pin
- Install the AR 308 rear takedown pin, safety selector, and the pistol grip
- Install the AR 308 trigger using a fire control group of modular design
- Install the AR 308 buffer tube
- Assemble the DPMS AR 308 buffer
- Install your selected AR 308 buttstock
Building Your AR-308 From an 80% Lower
As earlier mentioned, building an AR 10 .308 rifle from a .308 80% lower receiver is perhaps the easiest path to take. You should know that AR-308 lower receivers are a bit more complicated than AR-15 lowers as parts sourced from different manufacturers will not fit together like with the AR-15. Considering that none of the major AR-308 manufacturers sell 80% lower receivers, it’s up to companies in the 80% lower industry to develop compatible products and parts.
Opting to use an 80% lower for your custom build gives you the freedom to enjoy an easier and faster build with fewer frustrations. Considering that the DPMS platform is more common today, and the parts and components offered are more modular, it’s easier for you to build your rifle based on the DPMS platform for your AR-308 build. You, therefore, need parts that are DPMS compatible as they’re most likely to fit your lower receiver with or without slight modifications.
Most AR-308 80 lower receivers in the market today are designed to work with components from DPMS, Aero Precision, CMMG and other smaller companies that market their AR-308 components as DPMS compatible. The same goes for lower parts kit, upper receivers and other parts that should work right out of the box. As you learn how to build an AR 308, it’s important to understand that minor modifications will most likely be needed during the build process.
However, these modifications are not just limited to the lower receiver, but it’s the true nature of all AR 10 .308 builds. To go on with your lower receiver build, you’ll need a matching 80% 308 lower router jig to help you transform the lower into a firearm. After that, you can now pick up an assembled upper receiver and lower parts kit from your selected manufacturer. Assemble everything as required and ensure that all parts fit accurately to avoid functional issues.
For the buffer tube assembly and stock, you can purchase them anywhere with little concern about fitment issues. It’s important, though, to conduct some research. When assembling an AR 10 .308 for the first time, just make sure to keep the Dremel handy, and you’ll have no problems. If you get stuck along the way, you can always ask for help or watch tutorial videos from parts manufacturers.
Building Your AR 10 .308 Using a Gunsmith Kit
If you want to take the pain out of selecting and buying parts for your custom build, you should opt for a complete gunsmith kit that comes with the bulk of the common parts you need for building an AR 10 .308. This will free up your time as you work on the other assignments. You don’t have to buy expensive parts or a complete rifle. There are different manufacturers selling kits that provide the core parts of the AR 10 .308 which can then be combined with third-party parts to build the perfect rifle.
A good gunsmith kit should include a genuine lower receiver, upper receiver, barrel nut threads, lower receiver extension threads, trigger group and all the other parts needed to assemble the rifle. These custom build kits come with step-by-step instructions to help you every step of the way. Make sure to follow the guidelines to the letter. Otherwise, you will make a costly mistake.
There is no doubt that the AR 10 .308 is one of the best rifles out there in terms of power and range. According to 5D Tactical, a company that provides firearms enthusiasts the capability to easily and quickly finish 80% lower receivers for their AR 10 .308 builds, learning how to build an AR 308 can seem challenging, but with the right parts and components, you can easily build your own AR 308 rifle at home.
If you’re looking for quality parts and components for building an AR 10 .308, 5D Tactical is your trusted source for AR 10 .308 upper and lower receivers.