Getting to Know Your AR-15 Lower Receiver Options
You may have done your homework with regards to selecting the best lower receiver parts kit for your AR-15 project, but how much time have you spent learning about the lower receiver itself? Not only do you have options regarding how your receiver is manufactured, you can also choose whether or not you want to finish constructing it on your own.
Wait. So we found even MORE decisions for you to make?! You bet – but we would never leave you floundering. Sit back and relax while we help you to delve into the prolific world of AR-15 lower receivers.
Lower Receiver Materials
Aluminum AR-15 Lower Receiver
A vast majority of lower receivers are made of aluminum, which has long been the standard for AR-15 construction. If you are searching for the dependability of a “tried-and-true” material, these receivers are your best bet.
Polymer AR-15 Lower Receiver
Polymer AR-15 receivers began creeping into the market several years ago and continue to receive mixed reviews. To their benefit, they are slightly more lightweight than their aluminum counterparts and offer a wide variety of color options. Additionally, dings and gouges are more easily concealed on a polymer receiver due to the fact that they aren’t subject to corrosion or covered by a separate finish.
On the downside, polymer is subject to flex and may snap at weak points during installation of a AR-15 lower parts kit. According to some users, polymer receivers also require constant checks during firing to ensure metal pins haven’t dislodged from their holes in the receivers.
Although slightly less expensive than traditional metal receivers, it is our opinion that the benefits of polymer AR receivers just don’t outweigh the areas of concern at this time.
Hybrid AR-15 Lower Receiver
At least one company, MEAN Arms, has constructed a polymer and metal combination lower that is intended to be more lightweight and flexible then solid aluminum, but stronger at the notoriously weak points associated with polymer lowers. While the concept is genius, reviews of hybrid receivers are mixed.
Methods of Manufacturing Metal Lowers
Aluminum lower receivers are created using one of three processes: cast, billet or forged. Here are the main points you need to know about each of these manufacturing methods.
Cast
To create a cast receiver, molten aluminum is poured into a mold. Once hardened, the receiver is removed from the mold and finished using a computerized numerical control (CNC) machine.
Billet
To create a billet lower receiver, aluminum is rolled and compressed into a solid block. A CNC machine can then be used to cut out the shape of the receiver, making it one continuous piece.
Forged
In the forging process, aluminum is forced (or “hammered”) into dies to create the initial shape of the lower receiver. This requires a high level of compression, which reportedly makes the metal’s grain characteristics conform to the shape of the die. As a result, argument can be made that forging creates the sturdiest receivers. As with other methods, finishing is completed using a CNC machine.
Types of Lowers – How “Complete” Do You Want It?
Since you’re obviously interested in building an AR-15, maybe you’d enjoy finishing your receiver yourself as part of your project. Again, you have some decisions to make!
Complete Lower
A complete lower receiver will operate as a firearm once it is attached to an upper receiver. This means the machining process is finished, and the fire control group, magazine release, grip, buffer tube, buffer spring and stock have already been assembled prior to purchase.
Stripped Lower
A stripped lower receiver differs from a complete lower due to the fact that the stripped receiver does not have a lower parts kit installed prior to purchase. You will need to install the fire control group, magazine release, grip, buffer tube, buffer spring and stock.
80% Lower
An 80% lower means that 20% of the milling process is left unfinished. In order to complete this type of receiver, you will need to mill out and drill the compartment for the fire control group and selector switch. You will also need to drill holes for the hammer, trigger and trigger pins. Etching and anodizing are also customizable.
95% Lower
A 95% lower is akin to an 80% lower with one exception. On a 95% lower, the pocket in front of the buffer tube is pre-drilled, as this is sometimes a difficult area to complete with a drill press.
Federal Firearms Licenses and Serial Numbers
Once completed, the lower receiver is the sole portion of your project that is legally considered to be a firearm.
Purchasing stripped or complete lower receivers must be done via an FFL transfer requirements, and the receivers must be serialized. Conversely, 80% and 95% lowers are NOT subject to these requirements prior to purchase, due to the fact that they are incapable of accepting a lower parts kit until the milling and drilling processes are complete.
Should you choose to purchase an 80% or 95% lower, you are not required to complete an FFL transfer, nor is it mandatory for the receiver to have a serial number. This remains the case once you finish your AR-15 build, provided you intend to keep the rifle for personal use. If you decide to sell the firearm in the future, however, the sale is subject to FFL transfer requirements and must be serialized.
It is important to understand the legalities of building your own firearm, especially with regards to the lower receiver. Check out local, state and federal rules and regulations to ensure they coincide with the information provided here.
The Decision is Yours
As promised, we have now provided you with even more factors to contemplate as you plan out your AR-15 project. Regardless of the type lower receiver you decide to purchase, sticking with those marketed as “mil-spec” will likely give you the most consistent dimensions and tolerances for your build.
Once you have chosen the materials and manufacturing process that is right for you, you’ll be ready to decide how much “do-it-yourself” work you want to put into completing your lower receiver. Just don’t forget to have fun!
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