When you’re looking to build an AR-15 from an 80% lower, the first choice you’re going to have to make is which 80% lower you’ll build your rifle or pistol with. As you’ll quickly find out, there are different choices you need to make prior to selecting one. We created this Buyer's Guide to showcase the differences between forged, billet, and cast lowers, and the different kinds of aluminum alloys that make an AR-15 80% lower. Read on before buying!
Forged vs. Billet vs. Cast vs. Polymer 80% Lowers
First, we’ll take a quick second to explain the differences between forged, billet, cast, and polymer lowers.
Forged lowers are hammered into their final shape from a raw block of aluminum alloy. Since forging produces lowers that are dense, they’re also heavy. But they are also generally the strongest of the 80% lowers. These are commonly forged from 7075-T6 aluminum. That’s the same alloy the U.S. Military uses to build its M4 and M16 rifles.
Pick up a three-count of our Forged 7075 T6 80% Lowers while we can keep them in stock and get to building! This is a great way to hone your skills with your first build and perfect your lower with your second and third build.
Billet lowers start as one solid block of metal. Instead of being hammered into shape, they’re carved into their final shape. Since they are not made denser through forging, they are generally a little less rigid and tough. Most billet lowers are made from 6061-T6 aluminum, a slightly softer alloy that may dent or ding more easily. Rest assured, it’s just as combat-ready as a forged lower.
(Don't Buy Cast or Polymer Lowers)
Cast lowers are made by pouring molten alloy into a mold. As the alloy cools, it solidifies into its final shape. These are not nearly as common as the other types because the aluminum alloy and casting process can create pockets and inconsistencies in the final lower. This is obviously dangerous.
One other option is a polymer 80% lower. These are made from synthetic materials - usually a plastic amalgam. They are extremely light, but they’re also considered the least “robust” and they are more prone to cracking and deformation under hard use.
While there will certainly be people that disagree with us, we recommend sticking to either forged lowers or billet lowers. These are by far the most common, they’ve been proven in development and combat, and you really can’t go wrong with either. Polymer certainly has its place, just be aware it’s not as durable as the former two. We’ll say the same for cast lowers.
80% Lowers and Machining: Which Metal’s Best?
When you’re ready to buy an 80% lower, we recommend keeping a few different things in mind. We already talked about the strength of each material, but you must also consider the machining process.
Comparing the two aluminum alloys we mentioned, 7075 T6 has a tensile strength of 83,000 PSI. This is approximately twice as strong as 6061 T6. Polymer setups rate even lower. With a higher tensile strength comes better durability. While 7075 is stronger, it is hardened and more difficult to machine. If you’re a first-time builder, you’ll need to take your time and we recommend keeping some extra drill bits and end mill bits in stock for your first go-around with that 80% lower jig. A 6061 lower will be easier to machine, and it’s more forgiving if you make a mistake.
Forged vs. Billet Lowers: Weight, Looks, and Cost
If you’re primarily concerned with how the finished lower looks, billet receivers are much cleaner than forged receivers. Because they are finely carved, manufacturers can also add in some unique designs, like roll marks, flared bevels, and intricate trigger guards and mag wells.
Other factors to consider are weight and price. If weight is the primary concern of your build, we recommend going with a billet 80% lower.
In terms of price, billet and forged lowers are quite similar. There are plenty of options on the market, but the vast majority of both fall within the same general price range.
The Easy Jig Gen 2 is hugely popular with forged lower builders. Its design pre-measures every hole you need to drill, and its router guide ensures your end mill bits never touch the jig's steel plates! It's the easiest way to finish a forged 80% lower at home.
One final factor to consider is what type of tool you will be using to drill your lower receiver. If you are using a drill press, there’s no reason to not just go for a forged lower. However, if you are using a hand drill, it will be more difficult to drill into the forged lower, so you might consider billet unless you’re familiar with the build process. You can also invest in some hardened drill bits and end mill bits to ensure the machining process is easy.
Enhanced 80% Lowers
As you may have seen for sale, some manufacturers offer different levels of lower receivers. They may offer some that are pre-engraved with "FIRE" and "SAFE", or they may have some 80% lowers that have some of the holes for detents pre-drilled. Some also come with a trigger guard integrated into the lower itself. Our Premium Billet 80% Lower provides all these features.
When considering these types of lowers, it really comes down to personal choice. A good bit of this process really is personal choice, but with these advanced or enhanced lowers, the choice is really yours.
It should go without saying, but if you’re buying an 80% lower, you should also be sure to check out the manufacturer. Ensure that it is a quality company that offers good customer service. Your receiver should be protected against faults in manufacturing.DISCLAIMER: If you are new to the world of DIY AR-15 building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. We are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.