When I first got into guns, terms were confusing and I had tons of questions. Hopefully, I can help others learn more quickly than I did.
An AR lower, or lower receiver, is the bottom piece of the two-part receiver of an AR-15 or Modern Sorting Rifle. It is the part considered the actual firearm and requires a background check to buy from a licensed dealer. The Lower receiver houses the trigger system, safety, and attaches to the stock or brace of the firearm.
Want to learn more about lowers and the different types available? It’s actually pretty simple, I’ll show you.
This is What an AR Lower is for
The Lower receiver on an AR-style rifle Serves as the primary piece of the firearm frame. It’s no more important than other parts, but it’s the starting point and base of building an AR or Modern Sporting Rifle.
The MSR , or AR, has a unique 2-piece receiver. The receiver has both an upper half and a lower half. The upper half houses the bolt, firing pin, and barrel, and the lower houses the grip, stock, and trigger. The ATF decided that they’d consider the lower receiver the actual frame of the gun, so that part is restricted by communist, I mean federal law.
The lower isn’t anything special, to look at really. Most are pretty plain, but some do have interesting designs. Palmetto State Armory is well known for designing unique lowers following some popular topic or trend. Lowers are not designed to handle much pressure from firing the cartridge. They are more designed to hold the gun together.
A lower needs to be tough, resilient, and handle the shock of multiple firing. Some cartridges, like the 5.56/223, don’t have much recoil and can be used with a cheap or lightweight lower. If you are firing a heavy recoiling cartridge like 450 Bushmaster, you may want to avoid a cheap lower.
What are the Different Types of AR Lowers?
AR lowers are either cast, forged, or milled of billet. Most lowers are cast, or made in a mold, then finished with a CNC machine. Forged lowers are hammered into the basic shape, then finished on cutting machines. Some are completely machined from billet, a large piece of aluminum.
Cast lowers are the standard. They’re cheaper to make and work quite well. They are literally made by pouring melted aluminum into a mold to get the basic shape. This is quick but usually leaves minor visible mold marks. It also won’t leave as smooth of a finish as some prefer. Cast lowers are the industry standard.
Forged lowers are somewhat a marketing ploy really. It’s a much longer process to make, and they demand a premium price. Forged lowers do come out stronger, because the grain of the metal is consistent. They’re actually a good idea for a more powerful rifle.
Billet lowers are the most precise. They are completely milled out of a block of metal. They have the best fit and finish, and offer the most customization in the manufacturing process. Most of the lowers with unique designs are Billet machined lowers.
Lowers are made mainly from aluminum, but there are some polymer, stainless steel, and titanium ones. Aluminum is cheap, and strong, and works well. Polymer lowers are cheap and prone to breakage and increased wear. Stainless steel and titanium are expensive but very resistant to wear.
let’s talk polymer lowers for a minute. I’m all for cheap options that work. The polymer lowers are half-price of a cast lower, and very lightweight. They also seem to work. They do have some issues though.
They are not as durable as an aluminum upper. They are more prone to cracking and being crushed. Also, polymer, aka plastic, gets brittle in cold weather. They will not last anywhere near as long as an aluminum lower, and they are only $20 to $30 cheaper. I just don’t see it as worth it in my mind.
What is a Stripped Lower?
A stripped lower is a lower that doesn’t come with any parts of the trigger, stock, buffer tube, or safety. it’s just a single piece of aluminum. Some lowers come with all the parts in a kit, and some lowers come completely assembled.
If you are building your own firearm, you will probably buy a stripped lower. You will have to buy the parts to the trigger system, the safety switch with pin and spring, and the stock and buffer tube setup. You may also need to buy a trigger guard. Oh, and the magazine release and pistol grip.
What is an 80 Percent Lower?
An 80 percent lower is a lower that’s been roughed out but requires additional tooling before it is useable. They do not require a background check, since it’s not a useable lower without significant metalworking. 80 percent lowers require milling out of the trigger housing area and drilling holes for the trigger pins, requiring metalworking skills and tools.
An 80 percent lower can be bought and sold from the manufacturer with no federal restrictions since it’s not a functional lower. That means that if you buy and finish an 80 percent lower, it requires no background check and it’s not required to have a serial number if homemade and intended for personal use.
You can sell an 80 percent upper you have completed, as long as it was originally built with the intention of your personal use. You don’t need to add a serial number to your finished 80 percent lower if you later decide to sell it either as a complete firearm or just as the finished lower.
The difference between AR lowers and Pistol Lowers
Pistol lowers are much smaller than standard AR-size lowers. They are designed around the AR-9 platform, which is for mid-power pistol cartridges. Pistol and rifle lowers are incompatible with each other. The pistol lower will only handle short pistol cartridges like 9mm and 45acp, but the rifle lower will handle mid-length rifle cartridges like 5.56 and .223.
How expensive are AR Lowers?
Lowers usually cost between $50 and $150 dollars. The current rate is around $75 for a basic cast aluminum lower. Blem lowers can cost half that, but usually have small visible flaws like scratches or dark spots in the paint.
