The Best 80 Percent Lower for an Ultra-Light AR-15 Build

Posted by 80-Lower on Jun 12th 2019

The black rifle market is loaded with accessories and gear. Some of it might be cool, but all that stuff can seriously weigh down your AR-15. The original ArmaLite rifle was intended to be a lightweight, maneuverable shooter. Where other builders are packing on the pounds with rails, lights, buttons, and ninja stuff, we found it appropriate do discuss the opposite: Picking the best 80 percent lower for an ultra-light AR-15. We'll quickly break down the available 80 percent lower options, and we'll talk about weight and specs. Let's go!

How much does a regular AR-15 weigh?

A typical AR-15, weighing around 6.5 to 6.7 pounds.

To build an ultra-light AR-15, we have to first look at how much the average black rifle weighs. For this benchmark, we're sticking with the most common, bare-bones setup: A 16" barrel, standard A2-style handguard and flash hider, a carbine gas system, and a typical M4-style, six-position buttstock. The unloaded weight we came up with is an average of six to eight "store-bought" AR-15 rifles, each with the same components and configuration. Minor manufacturing differences contribute to a 0.2 range in average weight:

Standard AR-15 weight (unloaded): 6.5 to 6.7 pounds

Six-and-a-half pounds might not sound so bad, but once you start throwing on optics, slings, rail attachments, aftermarket muzzle devices and more, that weight can quickly climb. This is why it's so important to pick out the lightest core components of your AR-15 rifle or pistol. The core components include everything you need to build a functional AR-15 minus any accessories:

  • Gas system
  • Barrel assembly
  • Upper receiver
  • Lower receiver
  • Lower parts kit
  • Buffer assembly

Picking the lightest 80 percent lower

The foundation of your AR build centers on the lower receiver. This is the only part of your rifle or pistol considered a firearm, and it's the core component responsible for making your AR operate and cycle. Obviously, we're here to talk about building (not buying) your AR-15, so we're focusing on 80 percent lowers. There are three types of lowers to pick from:

A black anodized and forged 80 percent lower receiver for the AR-15. A forged 80 percent lower typically weighs around 10 ounces once machined.

Forged and billet lower receivers

These are the two most common lower receivers used to build an AR-15. Although forged and billet receivers are manufactured with different metal alloys and processes, their final weight is quite similar, around 10.4 ounces. Bother aluminum lowers are so similar in design and use that it ultimately comes down to personal preference.

Forged lowers are less expensive and feature simpler external designs. Billet lowers cost just a bit more and usually include aesthetic treatments or special features (an advantage of billet machining), like threaded fittings or integrated trigger guards. Forged lowers are slightly easier to machine, but wear out tooling more quickly.

The polymer 80 percent lower

a black, polymer 80 percent lower receiver and jig, used for building an ultra-light AR-15. The G150 Phoenix is an ultra-light polymer 80 percent lower, weighing around 4.8 ounces - half the weight of a metal lower.

Polymer lower receivers are relatively new, carving out a niche in the greater AR-15 market as a truly ultra-light alternative to aluminum lowers. These new polymer lowers initially received criticism and doubt, though many builders have put AR-15 rifles and pistols together with these units.

The results are impressive - and that's no surprise, considering the engineers behind polymer lowers went to great lengths to ensure they can handle rifle rounds and heavy recoil without failure.

Most importantly, the polymer lower provides a huge advantage over billet or forged lowers because of its weight: Coming in at around 4.8 ounces, this 80 percent lower weighs at least half a forged or billet unit.

Lightweight AR-15 parts to consider

Picking the perfect 80 percent lower is the foundation of this ultra-light build, but you'll need to consider the other parts you'll need to finish your rifle or pistol. You'll need to also pick out the following parts:

  • Lower parts kit
  • Buffer assembly
  • Barrel and gas system
  • Stripped upper receiver

To ensure you're getting the lightest parts available, we recommend looking at pistol components, titanium parts, and carbon fiber or polymer accessories. Your barrel will account for the bulk of your AR's weight (besides your upper and lower receiver), so we recommend investing in a lightweight, quality barrel before considering other parts' weights and costs.

AR-15 barrel weights compared

Pulling some basic product data from the market, we've found the average weights for different AR-15 barrel profiles (measuring 16", the common length). Barrels typically come with two gas block port diameters: 0.750", and 0.625". Barrels with the smaller 0.625" diameter will weigh less once assembled:

  • Lightweight (thin/pencil): 1 lb. 6 oz.
  • M4 (Government profile): 1 lb. 12 oz.
  • Heavy (HBAR): 2 lbs. 2 oz.

Remember, due to variances in manufacturers' barrel profiles, these numbers are just averages. Barrel weight will vary by manufacturer, steel, and final dimensions. Nonetheless, we can see how much of a dramatic reduction in weight certain barrel profiles offer. A lightweight/pencil barrel affords nearly one pound in weight savings compared to a heavy barrel.


  • Building an ultra-light AR-15 means departing from the usual parts.
  • A polymer 80 percent lower is the lightest lower you can find.
  • Titanium and skeletonized parts are the best way to finish your ultra-light build.
  • Using a polymer lower and pencil barrel will reduce your AR-15's weight by nearly half.

Now get to building!

DISCLAIMER: If you are new to the world of DIY gun 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. At, 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.