AR-15 Lower Receiver Aluminum Vs Polymer

The AR 15 Rifle has come a long way. When the AR series of rifles was designed by Eugene Stoner in the 1950s, they were made of aluminum. At the time, it was the metal of choice for spacecraft and jets, whereas many guns were still wood and steel. Stoner’s design was written off, for example, by the US Army as too light, leading to the adoption of the M14.

Something similar is happening again. Now it’s possible to get an AR15 lower made out of polymer, the new, light material of our time. Here, we’re going to walk through more traditional AR lower receiver construction as well as make the case for polymer receivers, along with some concerns that we still have about them. 

Aluminum Receivers

Traditionally, AR series rifles have had aluminum upper and lower receivers. Generally speaking, these are light and strong and get made in one of two ways. For most mil-spec guns, forged receivers have been common for years, and more expensive guns have had milled receivers. Both have had a long track record of performing well and standing up to the abuses often hurled at service rifles in particular. It’s the material used by Eugene Stoner in the 1950s.

As a metal, aluminum is light and strong, making it a popular component for firearms. In the AR upper receiver, it also bears a lot of pressure. But the AR lower receiver, which houses the trigger, magazine release, bolt release, and buffer, there’s no real need to be able to withstand the pressures of discharging a round.

Polymer Receivers

Polymer in firearms is not new. Glock, for example, has been making guns with polymer frames since 1982. Since then, polymers have gotten lighter, stronger, and are commonly used for many components that have to be durable over a long period of time.

Importantly, this use of polymer isn’t restricted to pistols. Rifles, too, have been made from polymer components for some time. For instance, the G36, a well-made German rifle that was adopted by several nation-states and is still in relatively common use, has a polymer upper and lower receiver, with only critical parts being made out of steel.

A polymer AR receiver, then, is not out of the realm of reason. Given that polymer has been successfully used in firearms design for going on half a century now, it makes sense that it would eventually come to the AR world.

We get that some people will be skeptical. To those folks, we’d ask that you carefully consider the design of the AR. Already, most of our handguards, foregrips, and stocks are made of polymer. All of those are parts that do not take pressure from the expanding gasses from firing. With that in mind, the next logical step in that evolution is likely to be polymer receivers. Yes, there have been and will be growing pains with this idea, but that can be said with any developing technologies.

In all likelihood, we expect to see an increasing proportion of ARs to come with polymer lower receivers.

Why Polymer?

In contemporary firearms design, especially in military small arms, the quest for the last 70 years has been for lightness. Taken from the lessons of WWII, many designers realized that contemporary infantry combat meant being mobile and putting down an overwhelming amount of firepower. This requires having a light weapon and the ability to carry a lot of ammunition.

The AR was an initial answer to that question: it was lighter than the rifle it replaced and fired a lighter bullet that was still effective during the majority of engagements. That’s what made it the fighting rifle of choice for so many countries for the last half-century.

Combat has not changed radically since World War II and has, I argue, become even more mobile. Now, urban combat dominates not only military action but also law enforcement and self-defense.

The same things that made the AR awesome in 1960 can be improved. The only parts of an AR that have to stand up to the heat and pressure of firing a bullet are the bolt, chamber, and barrel. This means that the upper receiver is likely to stay metal for the foreseeable future.

But, for the rest of the AR, as long as parts stay rigid, why not make them as light as possible. It would be silly, for example, to have a solid titanium foregrip. Sure it would be durable, but it would also add a pound to the weight of the gun. The same logic applies, I think, to the lower. 

Would I Buy A Polymer AR15?

In a word, yes. But that requires a little bit of context. Had you asked me in 2015, I would have been skeptical. I still am skeptical of, especially, 80% polymer receivers sold way too cheaply, and not usually by places with a good reputation. But, things are starting to change.

Recently, Brownells, a major gun retailer known for its customer service has started selling ARs under their own brand. Initially, this was under a Retro line, which has some of my favorite historical rifles as clone copies. Now they’re starting to sell a rifle designed with a polymer lower receiver and including an integral buffer.

Once major manufacturers like Brownells and others start putting more time and research into these, I’m willing to check one out. This is especially true with retailers that have warranties and would be willing to take one back if it does not function properly.

We’re still in the early days of polymer lower receivers to be sure. But, with that in mind, the history of polymer in firearms is already decades-long, and I don’t see it going anywhere any time soon. My recommendation would be if you’re curious to check out one.

Instead of buying an 80% receiver, you have to mill out yourself, leaving the polymer technology to an existing manufacturer is likely to leave you with a nice, reliable, light rifle that will be the start of the future in AR design.