Building an AR-15 might seem like a daunting task at first but in reality it’s a simple process – as long as you follow the steps and use the right tools. Tools are a definite issue; channel locks and a finishing nail are not what you need for the job (yes, I’m looking at you). Of course, part of the process is selecting good parts. There are myriad parts on the market. Take lower receivers, for example: how do you choose the best AR-15 receiver from the hundreds of options?
The lower receiver is the heart of your AR-15 build. Every other component revolves around it which is why it’s wise to choose one that’s well-made. It’s also the serialized piece of your build making it the one part that must ship to an FFL.
You’ll find a lot of AR fans say the lower is the least important part. Nothing but a paperweight, they say, so go ahead and buy whatever you want. In some ways they are correct; however, the lower is an integral part and if it isn’t machined properly your gun itself is one big paperweight. There are also different metals and styles to consider so rather than just randomly grabbing a lower off the proverbial shelf, take a moment and consider the following details.
Aluminum Alloys
There are two basic aluminum allows used for lower receivers: 6061-T6 and 7075-T6. 6061-T6 is more affordably priced and has traits such as a tensile strength of 45,000 psi, a shear strength of 31,000 psi, and a Brinell Hardness of 95. In contrast, 7075-T6’s tensile strength is 83,000 psi, shear strength is 31,000 psi, and it has a Brinell Hardness of 150. (Side note: Brinell Hardness is a method used to test in which an indenter is pressed into the material for a set time then removed. The indentation is measured microscopically. It’s the oldest hardness method still being utilized.)
Bottom line is 7075-T6 is almost twice as strong as 6061-T6 although the latter is technically more resistant to corrosion, a feature that is unlikely to count for much unless you intend to use a bare aluminum lower.
Methodology
Just as there are two basic types of aluminum alloys used there are three basic manufacturing methods. First is cast, the simplest method. Cast parts are made by pouring the aluminum of choice into a mold and allowing it to cool. Once it has cooled it’s machined into its final form. Here’s the thing about cast lowers: because the aluminum is poured into a mold in molten form and simply allowed to cool it is the weakest method of the three. That’s not to say cast lowers cannot be used; they can. Just keep in mind they aren’t as durable.
Billet is next on the list. Billet lowers start their life a solid block of bar stock extruded aluminum; the block is formed by being rolled by machine. From there it’s machined into the desired shape. You’ll find billet lowers tend to be the most highly-customized because the machining possibilities from bar stock are practically endless. On the toughness scale of the three methods billet falls in the middle.
The strongest method used is forging. A forged lower is hammered by machine into a forging die. Compressive force is used for superior strength; when that is done the raw form is finished by CNC. The metallurgy of a forged lower is stronger than cast or billet due in part to its continuous grain structure.
We’re not going to get into polymer.
Miscellaneous Tips
No, all lowers are not made equal. Use the above information to select the quality necessary for your task; is your AR-15 going to be for home defense, hunting, or long-range shooting? Do you want a flashy showpiece or a basic workhorse? Some lowers are not machined as precisely as others which results in poor fitment with the upper or, in severe cases, trigger assemblies failing to fit properly (or various vital holes being improperly aligned). Although it is not necessary to use the most expensive AR-15 lower receiver on the market you should take care to choose a quality, durable part. You want a reliable AR-15, right? Then select parts with care rather than haphazardly.
1. Anderson Manufacturing
Years ago, at one of my first SHOT Shows, I stood in the Anderson booth and listened to the whole spiel of the sales rep. To hear him tell it the company’s parts never need lubrication of any kind and have space-age durability. Reality is a bit different.
Anderson gets a bum rap from the snobby side of social media. There is some basis to claims of poor machining – sometimes a lower does hit the shelves that isn’t precisely machined – and it is accurate that they’re not quite as tough as some brands. But they do perform well within realistic expectations for the price point and are, in fact, more than satisfactory for thousands of gun owners. For new builders they’re even better because they don’t burn a hole in your wallet and they get the job done.
AM-15 Stripped Lower
Features: MIL-SPEC, multi-cal engraved, semi-auto, CNC-machined
Material: 7075-T6 forged aluminum
Finish: Type 3 Hard Anodized, Black
Treatment: Non-RF85
MSRP: $48.10, check it out here.
Budget restrictions often influence our choices on gun parts purchases but we do our best with what we have. I’ve used Anderson parts without any issues as have countless other AR builders. If you run into an issue simply contact their customer service and get it handled (or do some minor machining on your own). Odds are you won’t have any problems whatsoever. The Anderson lower is a good budget-friendly, entry-level option.
2. Aero Precision
Aero is a fantastic choice for builders of all experience levels. Their quality control is solid, parts are machined to precise specifications, and their customer service is great. In fact, I just finished a build using multiple Aero parts a couple weeks ago. There are more than a few Aero parts in my house, and it’s because I like them, not because they like me (I have no idea how they feel about me). These parts are well-made and well worth consideration.
The Gen 2 version of the Aero stripped lower has a couple features that make me favor it over others. The magwell is slightly flared an although that does lend it a cool aesthetic it’s really nice because it makes mag changes smoother. If you’ve ever fought with a lower during mag change drills you understand the thrill of smooth changes. It isn’t a luxury, it’s a necessity.
Another stellar feature of the Gen 2 Aero stripped lower is the upper tension screw. The lower ships with a nylon-tipped tensioning set screw in the grip tang that can be adjusted as needed for a snug fit against the upper receiver. Improvements in fitment are always a win.
Aero Precision AR-15 Stripped Lower Receiver, Gen 2
Features: Upper tension screw, flared magwell, multi-cal engraved
Material: 7075-T6 forged aluminum
Finish: Anodized Black
Weight: 8.35 ounces
MSRP: $63.00, check it out here
3) Rainier Arms AR-15 Forged Lower
Rainier Arms might not be quite as well-known as other companies but they do have a good reputation (and brand recognition is increasing, too). The company is based out of Washington State and manufactures a line of complete firearms as well as components so if you’d rather buy an already-made gun, go for it.
Their AR-15 Forged Lower is made using 7075-T6 aluminum and has a deep black finish. Features include a flared magwell and an upper-to-lower tensioning screw. This particular model holds appeal for me because it allows me to easily install the trigger guard I have on hand. And, of course, it’s also a quality, in-spec lower from a reputable manufacturer.
For those who favor Rainier Arms or are considering trying them out, keep in mind i1639 just passed in Washington State. Now might be the time to stock up (just saying). You can never have too many lowers on hand.
Rainier Arms AR-15 Forged Lower Receiver
Features: Flared magwell and upper-to-lower tensioning screw
Material: 7075-T6 aluminum
Finish: Black anodized
MSRP: $103.99, check it out here
4) Seekins Precision NX15 Skeletonized Lower
Lightweight builds have a number of benefits including the fact that they’re easier to carry on hunts. Don’t believe me? Try carrying 12 pounds of rifle through the mountains. It isn’t pleasant.
The Seekins Precision NX15 Skeletonized Lower is designed to cut weight from your build while also performing well – and it does. This is a billet receiver machined from 7075-T6 aluminum marketed as MIL-SPEC compatible made to strict tolerances. Features include an ambidextrous bolt release and an enlarged trigger guard. The lower is also Type III, Class 2 hardcoat anodized finished meaning it has a denser, more durable finish.
Seekins has a fantastic reputation for quality control and overall performance.They have quite a few fans in the AR building community, understandably so.
Seekins Precision NX15 Skeletonized Lower Receiver
Features: Skeletonized with ambidextrous bolt release and enlarged trigger guard
Material: 7075-T6 aluminum
Finish: Type III, Class 2 hardcoat anodized
Weight: 9.45 ounces
MSRP: $259.00, check it out here
5) Sharps Bros Warthog AR15 Lower
It’s impossible to put together this type of list without mentioning Sharps Bros. Whether or not you’re a builder you’re probably at least passingly familiar with the unique receivers designed by Sharps Bros – think aircraft-inspired lowers and Spartan-themed magwells. (Yes, they’re well-made, too.)
The Warthog AR15 Lower is one of their many creations and was designed in the spirit of the A-10 Warthog complete with snarling and tusks. The current iteration is the Gen 2 and weighs a bit less than the original. The Gen 2 also has a threaded bolt catch pin.
This lower is made from 7075-T6 aluminum and hardcoat anodized. The magwell is flared for faster magazine changes and has cutouts that help in reducing overall weight. Sharps Bros markets this lower as being MIL-SPEC compatible. They are known for putting out solid components machined to precise specifications so if you’re considering a lower with personality, check it out.
Sharps Bros Warthog AR15 Lower
Features: Flared magwell, threaded bolt catch pin, MIL-SPEC compatible
Material: 7075-T6 aluminum
Finish: Hardcoat anodized, black
Weight: 9.8 ounces
MSRP: $319.95, check it out here