Finding a lower is one of the first steps in building an AR-15 rifle. You might see a complete rifle you want to clone, a great upper, maybe a barrel, but before you get too deep into your build you need to pick out your lower.
Thankfully, lowers are nearly universal, finding the best lower is more a matter of your preference. There is a bit of difference between mil-spec vs a more traditional civilian lower, but mostly to fit the 1994 Assault Rifle Ban.
Finding the best lower is not difficult, but you will get what you pay for, thankfully we compiled the best lowers available
A lower is a Lower. The best AR-15 lower is the one you choose.
Cast, Billet, Forged, and Polymer
Cast, Billet, Forged, and Polymer are the manufacturing methods. Cast lowers are made in a mold; Billet is made from machining one piece of aluminum, forged is created by forging as much of the lower as possible before machining. Polymer is the odd man out as the injection molded plastics differ by company.
Cast Lowers are the cheapest but they do not handle the stress as well as the forged or the billet lowers. The other processes have also become cheap enough that cast lowers by manufacturers are hard to find but many DIY builders will cast their own lowers.
Forged Lowers are usually made from 7075-T6 Aluminum are a massive improvement over cast and some consider over billet. Mil-Spec for AR lowers is forged aluminum. Start by heating two blocks of aluminum to about 1/3 the melting point and then smashing it into shape with a truly massive hammer. CNC the lower to clean it up and you have a forged lower. The forging process changes the grain flow of the metal and creates an amazingly strong, yet low cost, after the initial investment, lower. Most big manufacturers use forged lowers in their AR-15s and most lowers available are forged. The classic lines of the M16 and M4 are there because the US Military requires forged lowers.
Billet lowers are for your more artistic builds and your smaller shops. They can innovate because they don’t require a complete change in the process only a few lines of code. Billet lowers are the most expensive because the manufacturers are taking the metal to the limit of their imagination. Billet Lowers are CNC’d out of one solid block of aluminum. Companies like Spikes Tactical took this to the extremes with several amazing lowers. But they are still novelty items compared most standard ARs. Billet Lowers also have unique stress points and different aluminum making them slightly less durable than forged lowers.
Polymer lowers are generally not the first thought of most AR builders. But we improvements in polymers and the success of Glock, it wasn’t long before the AR market found polymers have benefits for rifle builds, most notably the lightweight. Polymer AR Lowers are made in much the same way as forged and billet lowers. Getting a rough shape and then machining. But the material is much easier to work with only needing to support the end user for their use, coupled with the lightweight and the relatively small strain on the lower during firing. Polymer lowers are not new but they are gaining, however, they won’t stand up to punishment like a forged or billet lower.
The differences in lowers come down to quality and features. A high quality lower is built different, takes more punishment, has a more pleasing finish, or just is better machined. The most noticeable difference is only to be weight, and machining of the functional features. The weight of a high-end lower will be slightly lighter because more material has been removed during the machining process, but the lower will feel nicer, more pleasing. Like a well fitted suit. The fitted nature comes from the machining. Most low end lowers are machined in one pass of a CNC machine, leaving burrs and hand cutting angles. Mid-Tier will be finished in two passes smoothing the curves and removing the ridges, while high end will be almost molded to your hand.
Aero Precision is known for the effort they put into their product, you almost can’t beat them for the price.
A quick reference to look for is the beavertail machining. The beavertail is a cut that changes from the forged receiver to the CNC’d lower. A smooth transition with no solid edge is what you are looking for, with no burr marks or edges from the machining process creating a smooth fit for the fleshy part of your hand.
Trigger Guard Oversized vs Standard
Oversized trigger guards are becoming the new rage. Originally made for shooting with gloves, an oversized trigger guard allows for more freedom of movement. The largest draw is getting the trigger guard to precisely fit your hand with the equipment you want to use. A standard can be made to have more depth but not more length.
Standard trigger guards, like all standard features, have nearly 60 years of aftermarket support. If you purchase a lower with a standard trigger guard you can usually switch it to a nearly oversized by swapping a part and changing a few pins.
Read our AR 15 Trigger reviews here.
Magwell Flared or Square
Flared magwells are just that a wider opening to reload your magazine. The opening forces the magazine to slide in faster with
No one likes slop in their equipment. How nicely, beautifully or tightly parts fit together is one of the two major indications of quality. Building an AR-15 is no different but with the nearly infinite amount of lower manufacturers and upper receivers to bolt together. Some will be slightly out of spec millimeters.
Ambidextrous lowers allow you to quickly manipulate your rifle with either hand. This is a great for switching. Left handed shooters should look at not only ambidextrous lowers but also a left handed upper. Not only will you not get hit in the face by flying brass, but you will be able to shoot better with a rifle built for you. Right handed and left handed shooters will benefit by the ease of magazine changes and charging the rifle.
The downside is that rifle is most complex. Ambidextrous lowers fail the K.I.S.S test, keep it simple stupid. The addition of the ambi safety, magazine catch and bolt catch add weight and take up space in your lower. They get caught on bush, clothing, or sometime they can be mishandled. A standard lower can be used with either hand if you practice with it enough. Practice beats price every day of the week, and because the rifle has less parts they work better and last longer. You just have to decide if it is worth the tradeoff.
Skeletal lowers are usually billet lowers made to reduce as much weight as possible, often around the magazine. Skeletonizing is done to reduce weight at the expense of dirt entering the mechanisms. Yes, they are cool, but like most novelty guns, you have to decide if you can afford the novelty. Allowing dirt, mud, or debris to enter the AR lower will just cause trouble down the line. But the weight reduction can be huge with some lowers weighting as little as 6 oz.
Stealth Lower is a term for not having a massive ugly manufacturers marking or emblem on the lower. While some lowers like Colt, BCM, Noveske are prized and increase the value of the AR. Many companies are better served with stealth lowers to hide the fact of an AR build. Stealth Builds are usually within $5 of a marked lower and have no differences besides as few marking as possible. A keen eye will be able to read the companies name but most people won’t bother.
The other benefit of the Stealth lower is that you can have a custom laser engraving to personalize your lower without any of the intrusive emblems getting in the way.
Side folding ARs is a novelty that allows the AR-15 to use a folding buttstock through the use of capturing the recoil spring. They are great for building a small profile firearm, or for reducing the size of a long rifle into an easier to manage system. They only reduce the overall length by citation needed. But they are well worth it. The trade off and there always seems to be a tradeoff is that they don’t have the structural security of a dedicated buttstock. It can seem firm and will probably even support weight if tested but it will not be as strong as a rifle without the fold.
Match Upper and Lower
The mating surfaces of the upper and lower doesn’t change the accuracy of the AR-15. But no one likes a loose gun, it just feels inferior. You won’t be happy with a loose gun and when you aren’t happy you don’t shoot well and when you don’t shoot well you look to buy another gun. A matched Upper and lower will have a tight fit, this doesn’t mean that mismatched lowers will have loose fits but there is no guarantee.
A matched set is designed and engineer together. Your finish will match the upper and lower will match. The rifle will look closer to a completed firearm instead of a build unit.
Stripped vs Completed
A stripped lower, much like a good stripper doesn’t have anything on and it takes a bit of money to get her ready to play. While a complete lower is already deck out and ready to go. We recommend a stripped lower because you can dress her up exactly how you want, usually for less, and know exactly what makes her tick in case anything goes wrong.
Complete lowers are great if they already have the parts you want or are within a part or two of what you want for the same or a little less. Everyone that builds an AR knows just how annoying it is to be about done only to shoot a detent spring across the room and need to wait for shipping to fire your rifle. Complete lowers are ready to go as soon as you get them.
I will still recommend a stripped lower for your first rifle because you should learn what you can do with your gun and just how easy it is to build or repair her.
The Best AR Lowers
Aero Precision started off as an aircraft parts manufacturer that turned to the production of military equipment in 1993. Aero Precision are some of the most sought after lowers due to their quality and price. Several companies contract out to Aero Precision for their lowers and it may be worth looking into the different brands manufactured by Aero Precision if you are picky about your badging.
Probably the most recommended lower for building your own rifle in the history of the AR-15. Aero Precision is known for its quality. Some of the best machining you will see on a forged AR-15. Every M4E1 made by Aero Precision is worth the time investment in finding one available; 45 or 90-degree selector switch, tension screw to keep your upper and lower tight, and soft curves of 7075-T6 aluminum for comfort.
The problem is that with everything I love about this lower, and at a trip to McDonald’s over the PSA lower, it is nearly impossible to find for love or money. If you see an M4E1 for sale you buy it. It is probably the perfect lower
2. X15 Gen 2
The X15/AR15 Gen 2 lower from Aero Precision is nearly perfect. In fact while cheaper than the M4E1 or the same price as a PSA stripper lower, but it is only missing two features, the elongated trigger guard and threaded bolt catch pins.
The threaded pins make the M4E1 easier to build without roll pin punches, while the elongated trigger guard is a matter of preference. The X15 Gen 2 has one of the most sought after features of any AR lower, a tension screw to remove the slop when mating an upper and a lower.
Aero Precision makes a few more changes to the traditional AR Lower by adding threaded pin detent holes, allowing easier install of the buffer assembly. Everyone that has shot a detent pin while building an AR will love the threaded detent pin.
Brownells lowers hold a special place in my heart because I’m a kid from Iowa, where Brownells is manufactured.
The Brownells M4 Stripped lower, is like most others on this list a forged 7075-T6 aluminum lower, built to mil-spec. What makes the BRN-15 lower an amazing lower is the price and the quality.
Made in Iowa, in the heart of Midwest corn country, this lower is standard as standard can be. But the quality of the workmanship and low price make it enticing. Brownells is one of the best gun stores in the world with a staggering supply of unique rifle choices.
Palmetto State Armory
Palmetto State Armory grew out of 5 engineering and metal manufacturing companies with one aim in mind.
Put gun into Common Use, they want to sell as many AR-15s and AK-47s as possible to protect the United States against further infringement on the Second Amendment.
To that end, they offer a 100% lifetime warranty on PSA firearms. Thanks to their great customer service, low prices, and highly customization they are thought of as one of the best companies to buy any firearm, especially an AR-15.
4. PSA Stealth Lower
Forged 7075-T6 Aluminum to mil-spec with no roll mark, simple basic, low cost and available.
The PSA AR-15 Stealth is an AR Lower that won’t draw any attention. It is as common as can be, but it is low cost and sexy as hell on a rifle.
Unlike most AR Lowers you don’t need to worry about a giant emblem, on the side of your rifle just build it and shoot. Let your shots do the talking for you.
5. PSA Magpul MOE
Another Basic AR lower is the PSA Magpul MOE, everything you want in an AR and nothing you don’t need.
The only downside is that it has nothing interesting about it. It is boring, priced fair and you can’t go wrong with it.
There is nothing this can’t do but I do hate everything about it.
6. Shield Arms SA-15 Side Folding
Shield Arms has been making billet lowers for a while, what sets them apart is innovation.
AR-15s unlike the FAL, HK, AK, and G3 are not usually able to fold down their buttstock to fit into vehicles or smaller spaces. The AR requires a buffer spring in the buttstock to fire unlike putting the spring in the front of the gun like many other firearms. This leads to a bit less accuracy because the spring is not a straight push against the recoil of the gun. But these other firearms can fold down and even fire without unfolding the stock.
The Shield Arms billet lower, integrates the ability to side fold the buttstock and captures the buffer spring so that the rifle can fold. More importantly, it can fold without the awkwardness of an adapter.
The machined billet ensures a much tighter lockup than an adapter making the gun feel much better than an old rattle AK. The stock is actually so tight the first few times we used it we couldn’t figure out how to fold the stock it felt so tight.
7. Lead Star Arms
Lead Star Arms LSA-15 shows what a traditionalist can do with the AR-15 platform and a billet of aluminum. Lead Star using trusses to reinforce the lower while keeping weight down, using a Magwell grip CNC’d into the lower, Flared Magwell, and a unique oversized trigger guard.
The billet lower is amazing for AR builds if paired with an LSA upper. Unfortunately, the lower and mil-spec uppers don’t mix well because the lines aren’t matched up. LSA wants you to buy an upper from them and their uppers are great but it does narrow your options if you care about the lines matching on your upper and lower.
Anderson lowers are made from the same 7075-T6 aluminum, has about the same Type III Hard-Anodized Finish, usually at a lower cost.
I love Anderson lowers for the low cost when I was building my first rifle but then I like many others came around to thinking that the extra $50 I saved might not being as important as having a higher quality product. That isn’t to say that Anderson are the worst lowers, they are just the cheapest lowers that met mil-spec, and you would want as your gun.
Anderson lowers are every bit as durable as PSA or Aero Precision but they have a few more minor imperfections. A couple of burrs not hand ground, some rougher lines, the ability to slice open your hand while changing a magazine, are just a few reasons to spend more on your lower. But if at the end of the day Anderson is all you can find or afford, there is no shame in hand finishing your lower, or letting use round its lines.
8. Wilson Combat – WC-15
Wilson Combat has been high quality manufacturer of firearms since 1977, they have had a lot of time to perfect their AR platform and they are some of the best.
Bill Wilson had the idea that a billet lower could be made that would fit standard uppers and serve their lowers while keeping costs to the consumer, that’s you, low enough that anyone could afford to shoot. They have a passion and love shooters new or old.
The Unique parts of the BILLet are an oversized Magwell, trigger guard, and hex screw bolt catch retention. Bill also made sure to reinforce the aluminum where the gun receives stress. This allowed him to lighten the weight. The lower has an amazing finish and looks beefy next to the PSA lowers but the great thing is it looks good no matter what upper you use with it.
The Just For Fun Lower
9. Flightlite Raider SCR Pistol Lower
SCR Raider is a bit of a crazy idea, similar to the mare’s leg from Firefly; build a semi-automatic pistol, with a short barrel and a very short handle for an AR-15 pistol. But if you don’t see it yet there lies the beauty.
Nearly every other lower on the list is just another mil-spec clone but shooting this made me feel like a cowboy. Coupled with a 7 inch AR pistol barrel and a ten-round magazine, we had a gun just a bit heavier than some revolvers. Add in a red dot and you have a very fun, AR pistol that is surprisingly accurate.
Fightlite makes other great lowers as well the SCR is great for turning your AR-15 into a more traditional hunting rifle, especially in the areas where pistol grips and collapsing buttstocks are considered overthrowing the government.
Andrew Maurer is a Precision Rifle Series competition shooter and gunsmith. Building competition rifles for over 12 years. He works as a big game hunting guide in Iowa, South Dakota and Arizona. He is also a political scientist studying the effects of gun control on society. He teaches youth rifle shooting.