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How to Build an AR10

80 Percent Arms   |   Oct 11th 2021

There’s only a few reasons a person would want to have an AR-10 rifle: they’re planning on doing some long range, precision shooting; hunting, or it’s just because that DMR style looks so dang cool (designated marksman rifle). Either way, if you’re looking to build your Ar 10 from the ground up you’ve got quite a few decisions to make ahead of you and we’re here to help!

AR10 Build FAQ’s

Something that is not largely known about AR-10’s is that the name ‘AR10’ itself is a misnomer. There are two ‘patterns’ that you need to be aware of: LR-308 and AR-10. Technically, the AR-10 strictly refers to the initial design made by Eugene Stoner in the 1950s. So whenever you hear someone say “AR-10” today they’re almost certainly referring to the LR-308 which is also known as the DPMS pattern — the predominant amount of AR-308 80% lowers on the market are made in the DPMS pattern.

AR 10 Origins

Eugene Stoner original AR-10 design

The AR 10, or ArmaLite 10, was invented 30 years before the LR308 (or AR308). Eugene Stoner submitted the AR-10 as a bid for a military weapons contract in 1958 but once his patent had expired, companies took that opportunity to adjust the design which resulted in the creation of what we now recognize as ‘mil-spec’ standards. To further understand the difference between AR10 rifles and DPMS’ LR308, see our previous blog explaining that in detail.

AR10 vs AR-15: What’s the difference?

If you’re on the fence between a new DIY gun build project check out our previous blog that goes into the history of Armalite’s origins and how Stoner’s design snowballed into the massive AR platform that we know and love today. We go over the pros and cons of the AR-10 vs AR-15, their key differences and which one you should get.

AR10 Build Guide

As you embark on your DIY AR10 build journey, you’ll have to first decide on your AR 10 rifle’s intended purpose. This will inform you on what caliber and compatible parts or accessories you should choose to help you best fulfill that intended role and function.

Select an AR10 Caliber

First up, is caliber selection. The most common AR10 calibers that shooters choose from include the following:

    .308 Winchester - By far, the most popular, available and affordable round as far as AR10 calibers go. Has been in wide use since the 1950’s for militaries around the globe, big game hunting, long range precision shooting and competitions.

    7.62x51mm - The NATO standard round which is comparable to the commercial .308 Win, however, is slightly longer and can be shot out of a .308 rifle. You should not shoot .308 out of a 7.62 rifle. Think of it like how the 5.56 NATO is related to the .223 Remington.

    .243 Winchester - A popular sporting rifle cartridge that can hunt small to medium game and has higher chamber pressures, larger powder volumes and sharply tipped bullets that aid in creating terminal ballistics better than even what a .30-30 can do. .243 Win also has very low recoil along with a relatively flat flight path up to 500 yards.

    6.5 Creedmoor - Arguably the caliber that will one day, definitively, kill the .308 round as most precision shooting competitors today will decimate the competition in 1000 yard matches with this round. Only downside to this caliber when comparing 6.5CM vs .308 WIN is the ammunition’s availability and affordability with the lowest prices currently showing at $1.49/rd.

Select an AR10 Lower Receiver

This part is probably the easiest. Whether you choose to buy a 100%, completed AR10 receiver or to mill out your own 80% AR10 lower receiver, they will be directly compatible with any upper receiver or caliber you choose as long as it falls underneath the “AR10” category.

Select an AR10 Lower Parts Kit 

AR10 lower parts kit

Lower parts kits for AR15’s and AR10’s ARE different so make sure to buy the correct lower parts kit. As long as the product you’re looking at shows in the description it’s for an “AR10” or “AR-308” it will work with any of the four calibers we listed above. One of the cool things about AR10 lowers is that they can host a large number of calibers using the same lower receiver and internals such as the lower parts kit or trigger.

Select an AR10 Upper Receiver

AR10 stripped upper receiver

With the appropriate AR10-compatible caliber the upper receiver itself is not something you have to be too worried about when it comes to compatibility and fitment issues. However, you can choose to get some newer upper receiver designs like those that are lightweight or without a forward assist button.

Select a Handguard

 Mlok handguard for AR10

Also referred to as the ‘rail,’ you’ll want to make sure that your handguard is compatible with the selected upper receiver. Be aware that some upper receivers come with proprietary locking mechanisms that extend from the upper into the handguard. So if you buy your upper receiver from brands like Aero Precision or LWRC you may have to buy the handguards from the same companies as well. Upper receivers from 80 Percents Arms were designed inline with mil-spec requirements to be as universal as possible for accommodating a wider range of handguards.

Select an AR10 Barrel 

AR10 barrel in .308

Pick the barrel for your caliber! Pretty straightforward. You can choose any number of barrels with different inner linings, rifling or external coatings but the first consideration should be the desired barrel length. Knowing what barrel length you want will inform you on the types of handguards that would work best for you and what length those should be as well. For example, if you are going for a M110 clone/SR-25/AR10 build, you would need a 20” barrel from Knights Armament.

Select an AR10 Muzzle Device

 Aero Precisions AR10 muzzle brake

Going back to intended use, you should choose a muzzle device that makes sense for what activities you plan on doing. Maybe you plan on running suppressed? Is the rifle for law enforcement/duty use? Are you going hunting? Depending on your AR10 build’s purpose, you’ll have to select between a muzzle brake vs compensator vs flash hider. A lot of companies make them so doing your research beforehand will save you money and time to avoid unnecessary trial and error.

Select an AR10 Buffer Weight and SpringAR10 rifle length buffer weight and spring

Don’t forget your buffer system! For your convenience, we carry complete .308/AR-10 buffer tube kits that include the mil-spec buffer tube, end plate, castle nut, spring and standard buffer weight. If you want a heavier buffer weight to start tuning your AR10 build from the get go you’ll have to learn about the wide variety of AR10 buffer springs and weights. Check out our previous blog where we extensively explain everything you need to know — AR-10/AR 308 Buffer Weights.

AR10 Attachments

AR15 attachments, for the most part, will work for AR10 builds all the same. The only attachment that can be AR10 specific is the butt stock. While the mil-spec, 6-position buffer tube on AR15’s can be used on AR10’s as well, you’ll need A2 length buffer tube and appropriate buffer weight if you want to use longer rifle style stocks such as the fixed A2 butt stock or Magpul’s line of PRS butt stocks.

AR-10 Build Assembly

Before you start putting your adult legos together and mixing all the parts together make sure you have the following tools to help you have the smoothest possible build process:

-Armorer’s Wrench

-Gunsmithing hammer and punch set

-Needle nosed pliers

-Lower receiver vise block

-Vise

How to Assemble DIY AR10 Build

While vises are nice and make your workbench area look more legit, they’re definitely not necessary for the assembly of your LR308 lower receiver. One of the tricks I like to do whenever assembling or taking apart a lower receiver is to simply use a roll of packaging tape or duct tape. Sometimes all you need is a mat on a solid table to be able to reliably hammer in the pins for the trigger group.

Regardless of what tools you opt to make use of, once you have all of your AR10 components ready follow these steps to turn your lower into a fully functioning firearm:

1. Let’s start with the lower receiver. Install the magazine catch and mag release button.

2. Install the bolt catch spring and lever.

3. Install the front pivot pin. Don’t lose the small detent!

4. Install the rear takedown pin, safety selector and pistol grip. Each one of these parts is reliant on a small spring and a detent so make sure you use the correct ones accordingly.

5. Install the trigger group and anti-walk pins if you have them.

6. Install the buffer tube, end plate, castle nut, retaining pin, buffer weight and spring.

7. Next up is the upper receiver. If you bought a complete upper receiver then lucky you, not much else to do but slap that onto your lower receiver. However, if you bought all of your upper receiver parts individually then start by making sure everything is clean and to apply some lube to the threads for the barrel nut.

8. Install your barrel to the upper receiver. While tightening down the barrel nut, make sure it’s in perfect alignment with the gas tube.

9. Install the gas tube and gas block along with the barrel.

10. Install handguard.

11. Insert bolt carrier group and charging handle.

12. The completed AR10 upper receiver is now ready to be mated with the completed AR10 lower receiver. 

Build Your Own AR 10 With 80 Percent Arms

Ready to build your own AR 10? We have all the AR10 components, parts and accessories you need to complete a new Ar10 build! Before you get started, make sure you have an Easy Jig Gen 3 and Freedom Jig Router so you can quickly mill out an 80% AR10 lower receiver along with any other mil-spec AR9 and AR15 lowers on the market that you may purchase in the future.