Polymer, forged, billet, jig this, lower that – with so many options available in the AR-15 market, it’s tough picking the right parts to build your pistol or rifle. The root of the whole project is the 80 percent lower itself: You’ll be machining this unit into a functional, stripped lower receiver. You’ve got to make sure you do it right, lest you end up with a dud of a gun. So, what is the easiest 80 percent lower to build? Let’s find out:
(Don’t build an AR-15 with a cast lower)
Most 80 percent lowers fall into three categories: Billet and forged, or polymer. There are some cast lowers out there, but we strongly recommend against building with one. Cast lowers can end up with microscopic cracks, pockets, and fissures in the manufacturing process.
These imperfections have caused recorded instances of catastrophic failure (and the risk of potential injury or death) on the firing line.
Machining billet vs. forged lowers
Anyway, billet vs. forged. These are the two most common types of 80 percent lowers. So, which is easier to machine? You might not think it, but forged 80 percent lowers actually win this battle. Why? The answer can be found in the manufacturing process.
Billet lowers are cut and shaped from a larger piece of 6061 billet aluminum. Without any forging process, the grain structure of billet 6061 aluminum is more randomized. Billet lowers are also less dense. They carry particular advantages, though: Billet lowers can be made with more complex shapes and features. Our Premium Billet 80% Lower takes advantage of this by incorporating integrated trigger guards, threaded fittings for final assembly, and aesthetic treatments.
Why is forged aluminum easier to machine?
Forged lowers are hammered into their final shape with extreme heat and pressure. This produces a more aligned crystalline structure in the forged 7075 alloy. The result is a denser, more “orderly” metallic structure. Because fabrication is less expensive than CNC machining, our Forged 80% Lower is one of the most affordable options on the market.
When it comes time to machine with an 80 lower jig and end mill bit, forged 7075 chips better and
produces a more consistent, precise cut – sort of like mild steel. In fact, some machinists recommend not using lubricating oil if you’re making small cuts, usually 1/16th of an inch or less.
Billet aluminum tends to foul up the flutes on the end mill bit unless good lubricating oil is used while machining and cutting. Billet aluminum is also more susceptible to machining factors like rotational speed and heat.
Both are easy to build
Although forged lowers may be a tad easier to machine, either option will suit a first-time builder just fine. Both billet and forged require 30 minutes to one hour to complete, and all our 80 lower jigs include written instructions and video tutorials to help you along.
There is one more option to consider, however.
The polymer 80 percent lower
Great question! Polymer 80 percent lowers (like the G150 Phoenix) have only recently hit the market, but they’ve already proven their mettle in plenty of customer’s AR-15 builds. Polymer is essentially plastic, not metal. With such an extreme difference in material, is machining a polymer 80 lower even the same as completing a metal one? Is it any easier?
Yes and yes! In fact, you’ll be using the same tooling and bits to get the job done. Polymer 80 percent lowers include their own jig and tooling, so all you’ll need is a Dremel and hand drill. Aluminum lowers don’t always include their own jig and they require the use of a handheld router instead.
Polymer is the easiest lower to build
In case you hadn’t guessed by now, a polymer 80 percent lower is the easiest way to get your hands on a home-built AR-15 stripped lower. Polymer 80 lowers can even be finished with hand files and a manual drill. It doesn’t get any simpler than that.
What’s more, polymer is way more forgiving with different machining factors that aluminum alloy. If you’re nervous about putting power tools to metal, then polymer is a great alternative.
- Polymer, billet, forged – all are easy to complete. The jigs make them so! You’ll get instructions with any option.
- Forged lowers are more forgiving and a little easier to machine than billet. Polymer lowers are the easiest to complete.
- If you’re concerned about the durability of a polymer 80 percent lower then check out our last article, “Is a Polymer 80 Lower any Good?”