- 1 Everything You Need to Know About Stripped Lower Receivers
There’s a lot to cover about AR-15 lower receivers including legalities, materials, and manufacturing processes. We’ll do our best to answer all the questions you have below.
For those AR-15 newbies out there, let’s first be clear what a stripped lower receiver is.
Stripped Lowers – A stripped lower receiver is the serialized portion of an AR-15, making it the only part of the rifle that needs to be purchased through a licensed dealer (FFL). All other parts of your AR-15 can be bought online AND shipped directly to you, rather than to an FFL.
(Check Out the Best Lower Parts Kits to Finish Your AR-15 Lower Build)
It’s basically just a formed piece of aluminum that you’ll eventually add all of the other lower parts to, creating a complete lower receiver. By building your lower receiver, as opposed to buying a complete lower or a complete entire AR-15, you get to choose all the parts you want. In addition to allowing for full customization, you can sometimes save money building your lower rather than buying it.
For those apprehensive about building their first AR-15, building just the lower is a pretty good option; it can be done with fewer tools and there aren’t as many big errors you can make than when building an upper. Personally, I’m almost always fine buying a complete upper (depending on the build purpose), but always prefer building my own lower.
This article is focused on helping you find the best stripped lower receivers, though we’ll briefly touch on the other two options.
Complete Lowers – You can also purchase complete lower receivers that have all of the lower parts already installed, including:
Why would you buy a complete lower receiver instead of a complete rifle?
Buying a lower receiver and upper receiver separately can help you avoid paying the firearms excise tax. Another reason would be wanting a higher-quality lower than would be available in a complete rifle with the upper you want.
80% Lowers – 80% lowers are partially finished lower receivers that are missing the drilled holes for installing a trigger and safety selector. These are legal to purchase and use for an AR-15 build in most places—but always do your own research.
80% lowers can be shipped directly to your door, rather than to an FFL, because they are not technically a firearm yet.
I personally have not messed around with 80% lowers and have no plans to. They’re beyond the scope of this article, but it’s important you avoid buying one mistakenly if your intention is to instead buy a stripped lower.
I want to cover both my butt and yours, so always be sure to do your own research when building a firearm.
Disclaimer: I am not a lawyer. This article should not be interpreted as legal advice. It is the responsibility of consumers and readers of this to understand and comply with all federal, state, and local laws regarding purchasing or building a firearm.
The following points are simply what I’ve gathered from my own personal research and what practices I follow at the time of writing this, as a U.S. citizen. I cover both information for AR-15 rifles and AR-15 pistols. This is not necessarily an exhaustive list.
- It’s legal under federal law for law-abiding individuals to assemble a firearm for personal use, so long as that person is legally able to own the firearm they’ve built. You cannot manufacture firearms with the intent to sell them without being properly licensed.
- If building an AR-15 for yourself, a stripped lower receiver is the only portion that needs to be handled by a firearms dealer with a Federal Firearms License (FFL), as this is the serialized portion of the firearm. You can then purchase all of your other parts online and have them shipped directly to you.
- A factory new stripped lower receiver can be used to build a rifle, pistol, or carbine in any caliber, so long as you can legally own what you are building.
- If at any time a lower receiver has previously been used as part of a firearm, you cannot necessarily use it to build a pistol.
- If a stripped lower receiver is first used to build a rifle, you can no longer use it to build a pistol or handgun. A good rule of thumb is “first a rifle, always a rifle”.
- So long as a receiver is new, it is not necessary to have any caliber marking on it, and any caliber markings are irrelevant. Most manufacturers today mark their stripped lower receivers as “Multi-Cal” or something similar to avoid any confusion.
- To be safe when building a pistol, you can contact manufacturers and ensure your FFL transfers your stripped lower as an “other” item on the form 4473 or any other relevant forms.
- AR-15s with barrels shorter than 16″ or with an overall length of less than 26″ cannot have a stock or vertical foregrip attached to them if you are building an AR-15 Pistol. In the above picture of my AR-15 build, it does NOT have a stock or vertical foregrip. It does, however, have a pistol brace and an angled grip attached to the handguard, both of which have letters from the Bureau of Alcohol, Tobacco, and Firearms, and Explosives (BATFE) stating that they are able to be used on AR pistols (here & here).
- If you wish to build a short-barreled rifle (SBR)—a rifle with a barrel under 16″ or an overall length under 26″ that also has a stock or vertical grip—you must complete (and receive approval for) a form 1 through the BATFE and pay $200 tax stamp. You cannot build an SBR until being approved to do so.
- If you’re building an AR-15 with both a barrel length of 16″ and an overall length longer than 26″, you can attach a stock and/or vertical foregrip—the same way you would be able to purchase a complete rifle with those accessories attached (no additional paperwork or legalities). Remember though, you cannot then use that lower receiver to build a pistol.
(Check Out the Best AR Pistol Braces Here)
Aluminum – Most lower receivers you’ll come across will be made out of aluminum, as it’s relatively lightweight, strong, and affordable.
There are, however, different alloys used in aluminum receivers: 6061 (T651) and 7075 (T651).
6061 (T651) vs 7075 (T651) Aluminum Alloys
|Aluminum Alloy||6061 (T651) Aluminum||7075 (T651) Aluminum|
|Tensile Strength||45,000 psi||83,000 psi|
|Yield Point||40,000 psi||74,000 psi|
|Elongation at Break||12%||10%|
|Shear Strength||31,000 psi||48,000 psi|
|Thermal Conductivity||170 W/m-K||130 W/m-K|
|Strength to Weight Ratio||115 kN-m/kg||196 kN-m/kg|
I’m not going to lie and say I fully understand all of this, but I know enough to understand that 7075 (T651) is stronger, harder, and better. Considering you don’t save much money by going with the inferior option, you might as well go with what’s best.
Polymer – If you’re looking for a concealed carry pistol, most options these days have polymer frames. With that said, it’s probably not a good idea to get a polymer lower, even if they are often a lot cheaper.
AR-15s, compared to pistols, will put a lot more stress on the polymer, and there’s a higher chance of it breaking than I’m personally comfortable with. You will not see any polymer lowers in my gun safe any time soon.
If you search the internet for “broken polymer lower”, you’ll see that they usually break like this because all the stress is where the buffer tube screws into the lower receiver.
Titanium & Steel – If you look hard enough you can find these, but there’s really not much point in getting them. Both are going to be stronger than aluminum, but steel is unnecessarily heavy, and titanium is unnecessarily expensive.
Aluminum is more than capable to be part of your “bombproof” AR-15.
Ok, so now we know that we’re looking for 7075 (T651) aluminum lower receivers. But how do we want them to be made?
There are three types of manufacturing processes for AR-15 lowers: cast, billet, and forged.
Cast Aluminum – Casting is a process in which molten aluminum is poured into a mold.
Cast lowers are usually the cheapest available option; however, many manufacturers of cast lowers have a bad reputation for poor quality control, and regardless of how well they’re cast, they’re still going to be the weakest lowers of all three options.
Billet Aluminum – Billet aluminum lower receivers are cut from solid blocks of aluminum, as shown in the picture below.
They are stronger than cast receivers, though not as strong as forged receivers. They do, however, allow for the guard to be included in one piece with the rest of the lower and allow for some pretty uniquely designed lowers.
For example, the Sharps Bros Warthog lower receiver:
Forged Aluminum – Forged aluminum lower receivers are “hammered” into their shape by compressive forces. This results in the strongest aluminum lower receiver possible.
Knowing the above, you should have a good understanding of why we recommend forged 7075 (T651) aluminum 7075 lower receivers for the vast majority of AR-15 builds. The only exception would be if you wanted a uniquely designed billet lower.
Generally, I opt for whatever is cheapest that fits these criteria, so long as it’s from a reputable manufacturer. Some of you may also want to factor in small stylistic differences, like the way various manufacturers’ logos look etched into the receiver.