While having a 300 BLK build can mean simply having a dedicated 300 BLK upper receiver and a normal AR15 lower borrowed from a previous gun, having a 308 AR means you have to do an entirely new build separate from an AR15. A new complete build involves new AR10 lower. But what if you lived in a state that doesn’t require you to go through an FFL for a lower? What if you can acquire an AR10 lower without any form of registration or dealer record of sale? Residents of non-restricted states, I introduce you to the AR10 80 lower.

For some shooters that enjoy the modularity of Eugene Stoner’s AR-15 legacy, 5.56 NATO and 300 Blackout might not cut it in terms of firepower. While the AR-15 was originally designed for 5.56×45mm, the AR-10 predecessor was actually made for 7.62×51mm. 308 WIN and 7.62×51mm both serve as an excellent long distance cartridge in semi-auto fire. So if you’re looking to get into precision shooting want to build your own AR10 lower here is our comprehensive guide to AR10 80 lowers.

AR-10 vs AR-15

The AR-10 performs in a class separate from AR-15. While the AR-15 serves a very modular role as a lightweight small-caliber carbine, the AR-10 and SR-25 pursue a shooting philosophy closer to that of a sniper rifle or designated marksman rifle. The question for whether the AR-15 or AR-10 is the superior rifle system for you should be more related to what your mission type is.

Hog hunting trips may be accomplished with your AR-15, but killing large game with confidence that you’re delivering sufficient bullet energy from 300+ yards away would call for calibers like the .308 Winchester or 6.5 Creedmoor. Fair warning: the build cost and rounds for an AR10 can be exceptionally more expensive than building and shooting an AR15 (and that’s not even including an long range optic yet). However, complete budget builds will always be more affordable.

AR-10 Lower and AR-15 Lower Parts Compatibility

When looking at an AR10 stripped lower next to its AR15 counterpart, you’ll notice that an AR10 lower receiver is longer and more elongated. Where the buffer tube ring meets the rest of the AR10 lower has more distance compared to the AR15 lower. Although the function and design of the AR15 lower and AR10 lower are similar in just about every way, the AR10 is scaled up in dimensions to support higher cartridges. It’s for this reason that lower parts kits (besides the grip) aren’t interchangeable between the two platforms. Additionally, the following parts generally aren’t compatible between an AR15 lower and AR10 lower:

• Upper receiver
• Barrel and barrel nut
• Bolt catch
• Muzzle device
• Magazine catch
• Rifle buffers
• Lower parts kit
• Handguards/Rails

80 Percent Lower

An 80 percent lower receiver is a billet of aluminum that is in the shape of a lower receiver. It does not meet the ATF’s definition of a firearm. An 80 percent lower lacks a machined out pocket for the fire control assembly and will not function without the last “20 percent” of milling done. As such, you can buy an AR10 80 lower or any 80 lower without the need to go through an FFL and even have it shipped to your front door directly in most states.

Only after you’ve milled out the space for the trigger pocket and drilled the appropriate holes for the safety selector in the lower receiver that you have what meets the definition of a stripped lower receiver. For left handed shooters or shooters expecting to switch hands in a tactical scenario, it is worthwhile to explore 80 lowers for building out ambidextrous lower receivers.

AR-10 Lower Materials

Materials science and engineering has come a long way from the days of Eugene Stoner. There are a variety of materials to choose from for an AR10 80 lower receiver with each specializing in different balances of corrosion resistance, cost efficiency and durability.

Polymer AR-10

Polymer and other materials like reinforced nylon have grown in popularity for those looking to reduce weight. InRangeTV’s rendition of ‘What Would Stoner Do’ rifle has taken up to bring back the AR-15 to its principle roots of a lightweight fighting carbine with modern durable polymer material as the basis for the KP-15 lower receiver. One popular option for polymer AR10 80 lowers is the .308 80% Polymer Lower Receiver by James Madison Tactical.

Polymer material for lower receivers have been a controversial subject with the spotlight on plastic’s durability. Sure you’ll have less weight to be burdened with and don’t have to worry about corrosion or scratches on the receiver, but what if you run over your gun or drop it? What if your gun is walking alone at night and God forbid, it encounters a gang of polymer-phobic hammers? Well fear not because good, old-fashioned, non-ferrous aluminum is here to have your back.

Aluminum AR-10 Lowers

Aluminum receivers usually come in either two different aluminum alloys, 6061-T6 and 7075-T6. The numerical four digits indicates the alloy’s primary mix. 6XXX tells us that the alloy has a majority mix of magnesium and silicon, while 7XXX tells us that the alloy holds a majority concentration of zinc. The following T6 means that the alloy type has been aged and heat treated to relieve stress and prevent potential distortion during machining.

For options on aluminum AR-10 80 lowers, check out what we have available in anodized and raw, 308 80% Lower Receiver - Billet - Black Anodized and 308 80% Lower Receiver - Billet - RAW.

6061-T6

6061-T6’s properties are more malleable and more resistant to corrosion compared to 7075-T6. You will have a slightly easier time milling an 80 lower made from 6061-T6 aluminum. The softer properties of this alloy would have less wear on your tool bits especially if you plan on doing many 80 lower receivers. However, the corrosion resistance would not be noticeable unless your receiver already has a protective coating. Some people would rather not have bare aluminum shown on the surface but best practices involve painting the receivers after it’s been milled out and completed. If you are most people, the edge of 6061-T6 over 7075-T6 largely ends only with a lower entry cost in time and money.

7075-T6

7075-T6 is the mil-spec option that has twice the strength compared to 6061-T6. Its popular applications include aerospace and maritime vehicle engineering as it’s sturdy enough to be comparable to many steel alloys and is commonly found in airplanes and naval vessels. Although this mix of aluminum is significantly stronger and slightly lighter, most of the force from a catastrophic failure in an AR system tends to go through the upper receiver and the magwell.

There are also speculations that in the event your firearm explodes, softer materials might be preferred. A softer metal AR10 lower in a firearm that explodes is more likely to hold more of itself together and bend rather than expand into itty bitty pieces of shrapnel. Regardless of what type of aluminum you choose for your AR10 lower, obviously, we never want the gun to blow up. To achieve such pressure build up, however, is unlikely to ever be achieved on the civilian side of AR10 ownership.

Unless a moron decides to attempt to fix a barrel obstructed by a squib round by shooting several overcharged rounds through it, there should be no concern for a catastrophic failure of that level to occur. Should you however be concerned about roving packs of aluminum-phobic sledgehammer thugs or a vehicle accidentally running over your gun, the 7075-T6 is an excellent choice for durability.

What do I need to finish an AR-10 80 lower?

First, take a look at the material you’ve chosen. Your tool bits and drill/router must be rated to work with the material of the AR10 80 lower. Polymer lowers are soft and you’ll have an easy time tooling your AR10 80 lower with lower end routers. For those looking to mill out AR10 lowers that have a harder construction, you might want to pack some spare tool bits if you’re going to be doing this often. Having addressed that, you will need the following items:

• Router
• Jig
• AR-10 80% Lower Receiver
• Drill bits and end mills

For using our Router Jig Extreme, you will be able to mill out your AR-10 80 lower in minimal time with no experience needed. Check out this guide on using our jig, How to Build an 80% Lower | AR-15, AR-10, AR-9, for further reading. Just to be safe, pick up some spare end mills in case your first one chips a tooth or if you get addicted to this new hobby.

AR-10 Stripped Lowers

If it doesn’t bother you that government agencies know what firearms you have and you’d prefer to save time you could always opt for a complete AR10 stripped lower. Completed stripped lower receivers are considered as firearms by the ATF which is why their purchase requires a background check. Building out your own AR10 80 lower in the current economy can easily cost you more but you get to skip the 4473 Form and you get to choose how budget or fancy the components will be. If the benefits of an 80 lower won’t make a difference for you then you’ll still have a wide variety of choices for an stripped AR10 lower receivers.

Aero Precision M5 AR308 Lower Receiver - $204.99-234.99

If you’re looking for the equivalent of a Camry that will get the job done and last, we’d skip Anderson Manufacturing and Palmetto State Armory by going directly to the Aero Precision M5 AR308 Stripped Lower Receiver. Aero Precision has become a staple name for military specified adequacy and reliability at reasonable cost. You wouldn’t find any excessive machining marks and can feel reassured in their high quality control and tolerances.

BRN-10 Lower Receiver - $314.99

Tooled from a dense alloy of 7075-T6 aluminum, Brownells presents their version of “What Would Stoner Do'' with the AR10; the BRN-10® Lower Receiver is a closer rendition of the original AR10 using modern capabilities in material engineering and machining. This is a proprietary lower that only fits a BRN-10 upper receiver. True to Stoner’s design, the upper receiver for the BRN-10 also does not include a forward assist button. If you’re interested in being able to fondle the manifested dreams of Eugene Stoner now made possible by the lack of politics and with modern technology, this AR10 lower is for you.

LMT AR-10 Lower MARS-H - $539.00

At the top of the line we have the ultimate flex on poors: the LMT AR-10 Lower MARS-H from Lewis Machine & Tool Company and their Modular Ambidextrous Rifle System - Heavy. If buying a $500+ completed and stripped AR10 lower, which is a dedicated fit for a $1169 AR10 upper (not including the barrel), is your goal... this is the first and last AR10 receiver set you’ll want to buy. The MARS line is the latest breed of battle rifles to come from LMT and is also the successor to their Defender series which also now features ambidextrous controls.

Build your own 80% AR10 lower receiver with Modulus Arms!

As you can see, purchasing a completed, although stripped, AR10 lower can be extremely expensive depending on where you get it from. The best AR10 lower receiver is going to be an 80 lower from Modulus Arms as it only costs $139.99 and can be completed with the Router Jig Extreme in very little time with no special expertise or experience prior! Just follow the instructions in the manual and you’ll have a completed AR10 lower in no time at all.

Keep in mind, technically, what we have is an LR308 80 lower meaning For any additional advice on what power drill our hand routers to use, contact our customer service team to clear up any questions you may have.