Are you looking for the best lower receivers for your M4? If so, you’ve come to the right place.
Best Budget Pick: KE-15 Stripped Lower Receiver
The KE-15 Stripped Lower Receiver is a good pick for a budget lower receiver. Built out of lightweight and yet durable 7075 aluminum with a hard coat anodized finish, it comes ready for you to customize to turn into your own complete upper.
Best Stripped Lower: BRN-4 Stripped Lower Receiver
The BRN-4 Stripped Lower Receiver is a solid if also expensive choice. Built to the same shape of the HK416 lower receiver while still being fully compatible with the AR-15, the BRN-4 is very durable and rust resistant thanks to its hard coat anodized finish.
Best Complete Lower: PSA AR-15 MOE EPT Complete Lower Receiver
The PSA AR-15 MOE EPT Complete Lower Receiver is a solid choice for a complete lower receiver for your M4 or AR-15. It’s built out of a rugged and yet lightweight aluminum material, and also comes with an excellent trigger.
If you are planning on upgrading your M4 or building a new M4 from the ground up, the lower receiver is one of the most important components to invest in.
In this guide, we’re going to dive into the top three best lower receivers for an M4. In addition, we’ll discuss the different parts that make up the lower receiver, the primary types of lower receivers that are available on the market, and the top qualities to look for in a lower receiver as well.
We’ll also dive into what the primary differences are between an M4 and an AR-15, as the two terms are often thrown around interchangeably.
What Is The Difference Between An M4 and an AR-15?
What is the difference between and an M4 and an AR-15? The biggest difference lies in the fact that the M4 is a select fire weapon that can alternate between semi-automatic or fully automatic, while the AR-15 is a semi-automatic only.
Sometimes the two terms are interchangeable to refer to the same weapon. For instance, Colt often refers to their semi-automatic AR-15s that they sell to American civilians as M4s as well. An example is the Colt LE6920 semi-automatic AR-15, that is often labeled as a Colt M4 despite being semi-automatic only.
The M4 can trace its roots back to the XM177 carbine. When the M16A1 was issued as the standard service rifle for the United States military during the Vietnam, the shorter and more compact XM177 was released afterwards as well. The XM177 eventually evolved into the M4 in 1984, before becoming formally adopted into the United States military in 1991.
The M4 and its successor the M4A1 quickly gained favor due to being a lightweight and more compact alternative to the M16, and they were favored in urban environments especially. By the mid-2000s, the M4 had been adopted for the entirety of the United States armed forces. The M16 is currently being phased out from frontline use in favor of the M4 due to its overall smaller size.
United States civilians can own fully automatic or select fire M4s under current law, but only with the appropriate licensing requirements. Since the M4 and AR-15 are virtually identical, the components between the two are essentially the same as well. The lower receiver you buy should work for both the AR-15 and the M4, although it is your responsibility to confirm this as such.
What Parts Make Up The Lower Receiver?
There are many key components that make up a total lower receiver. Take note that there is a difference, as we will explore later, between a stripped lower receiver and a complete upper receiver. Complete lower receivers come with literally everything installed that comprises the lower receiver, while stripped lower receivers lack all of the components needed and require you to install them yourself.
For the purposes of this discussion, here are all of the components that consist of a complete lower receiver:
The trigger assembly is one of the most essential parts of your lower receiver, because without it, you could not even fire your rifle in the first place. The trigger assembly includes the trigger, pins and springs, and the housing.
The magazine catch hooks into a slit in the magazine so it can hold in place. Without the magazine catch, your lower receiver would not be capable of holding onto the magazines, and the entire weapon would be rendered nearly useless.
Most AR-15s and M4s come installed with a pistol grip. This allows you to properly hold the rifle in order to fire it. Take note that some jurisdictions, such as California, forbid the use of pistol grips and will require you to use a California-compliant grip instead.
The stock is what you press against your shoulder in order to gain stability when firing the weapon. Also, inside the stock includes the spring and the buffer tube, both of which are needed to fire the weapon as well.
Lower Receiver Housing
Finally, the lower receiver housing is the main piece of the lower receiver that houses all of the other components. Most of the time, a stripped lower receiver will consist of just the lower receiver housing and no other components.
Types of M4 Lower Receivers
There are many types of lower receivers for the M4 as well that we need to discuss. These are:
Complete Lower Receivers
Complete lower receivers, as previously mentioned, are literally complete lower receivers that come with everything you need. In other words, a complete lower receiver comes ready to install with a complete upper in order to create a complete M4 or AR-15. Complete upper receivers do not require you to add anything else to them and they are ready to go.
It should be noted that as complete lower receivers are ready to install, they are considered to be a firearm already in accordance with United States Federal law. This means that the associated sales restrictions will take place. If you want to purchase a new lower receiver, chances are very good that you will need to go through an FFL. You almost certainly will need to have it transferred via an FFL if you are going to be ordering it online.
Complete lower receivers are also usually more expensive than stripped upper receivers since they come with everything already installed.
Stripped Lower Receivers
Stripped lower receivers refer to any kind of M4 lower receivers that are not yet ready to combine with a complete upper in order to build a rifle or carbine. There will be more parts that you need to add to the receiver itself in order to transform it into a complete rifle.
The overwhelming majority of the time, the stripped lower receiver will not have any components at all other than the stripped receiver housing. It’s your responsibility to purchase all of the other components that you need and install them. Otherwise, you can purchase the components on your own but then have a gunsmith install them if you so choose.
However, the stripped lower will have all of the holes and slots from the manufacturer ready to go. This means that if you buy additional drop-in components, you can fit them into your stripped lower receiver with very little fitting work required.
The main advantage to a stripped lower receiver is it gives you the easy ability to customize your M4 as you see fit with other parts of your choice. The downside is that it’s not ready to go out of the box, and you also need to do your research to make sure that any and all other parts you buy are compatible with your stripped lower of choice.
Forged Lower Receivers
Forged lower receivers are among the most common on the market. They are very durable and strong, but also higher prices than a billet or polymer lower receiver. They are usually built from a heat hammering process before being distributed out to other vendors.
Billet Lower Receiver
A billet lower receiver is usually built out of aluminum billets. These are lightweight lower receivers that are commonly used in precision rifles, and a lot of labor goes into their construction. A billet lower receiver will usually allow for more customization options than a forged lower receiver, even if it will also usually be less durable.
Polymer Lower Receiver
A polymer lower receiver is a lower receiver that is built out of hardened polymer using an injection molding process. It’s the same kind of durable and yet lightweight polymer that is commonly featured on modern day duty pistols like the Glock pistol or the Smith & Wesson M&P. Polymer lower receivers are almost always much lighter than their steel and aluminum counterparts.
80% Lower Receivers
Remember how we noted that complete upper receivers are considered to be a firearm and are treated as such under US Federal Law? An 80% lower receiver, also known as an unfinished receiver, is a receiver that is not considered to be a firearm under current law.
The biggest difference between a stripped lower receiver and an 80% one is the fact that the 80% lower receiver does not have a serial number on it, which makes it untraceable. It is literally not regulated by law, and you will not need to go through any background checks in order to buy one.
However, an 80% lower receiver will require the aid or services of a gunsmith to get it working and other parts installed, assuming that you’re not a gunsmith yourself. Still, this is a minimal price to pay in exchange for getting a lower receiver that cannot be tracked by the government.
Buyer’s Guide For The Best M4 Lower Receivers
These are the most important factors to consider when looking for a new lower receiver for your M4:
Type of Lower Receiver
First and foremost, think very carefully about the type of lower receiver that you want to get. Refer to our discussion above.
The build quality of your M4 lower receiver is vital to ensure that it will be well-made and long lasting. 7075 aluminum in conjunction with a hard coat anodized finish is often considered to be the gold standard for a lower receiver because aluminum is both durable and lightweight, while an anodized finish is very rust and corrosion resistant to further ensure good durability.
Stripped or Complete?
Remember that you will always need to choose between a stripped or complete lower receiver, or one that needs you to add components to or one that is ready to install right out of the box. Do you want a lower that you can customize further, or do you want one that will require little to no work?
The 3 Best M4 Lower Receivers For 2020
Now that we’ve covered why you need to upgrade your M4 lower receiver, here are our top three choices for the best M4 lower receivers for 2020:
PSA AR-15 MOE EPT Complete Lower Receiver
The PSA AR-15 MOE EPT Lower is an aluminum forged receiver that is built slightly differently from other mil-spec AR-15 lowers. It comes with a smooth nickel finish that should help it to fit nicely in other AR-15 upper receivers. It’s also designed to function well with virtually any kind of common AR-15 ammunition.
The trigger on the PSA is also much smoother than most standard mil-spec triggers, which by itself makes it worth upgrading. Even though it is a bit expensive, the PSA is well worth the money you’ll invest into it thanks to the fact that it is a durable and lightweight receiver option.
Finally, as this is a complete lower receiver, it comes with everything you need already installed, and is ready to merge with a complete upper receiver to create a complete M4 or AR-15.
All in all, the PSA AR-15 MOE EPT Lower receiver is a solid choice if you are looking for a complete lower receiver for your M4 or AR-15. It’s lightweight, durable, and comes with a phenomenal trigger that is much better than most mil-spec AR triggers.
- Trigger is much smoother than with mil-spec models
- Compatible with most types of AR-15 ammunition
- Built out of lightweight and durable aluminum
- As a complete lower receiver, it comes with everything you need
- A little expensive
BRN-4 Stripped Lower Receiver
If you would prefer to have a stripped lower receiver that comes ready for you to easily customize, you will want to take a close look at the BRN-4 Stripped Lower Receiver. This stripped lower receiver is forged out of the same shape that the German-made Heckler & Koch HK416 carbine is designed for.
However, it’s also designed to be as closely authentic to the AR-15 as it can be. If anything, the BRN-4 can be best described as a combination between an AR-15 and an HK416 lower receiver, but it will still be a solid option for M4 enthusiasts.
As a stripped lower receiver, this receiver does not come with all of the parts needed for you to pair it with an upper receiver yet. Instead, you’ll need to buy additional components and then install them yourself.
Overall, the BRN-4 is a solid pick for a stripped lower receiver. It may be expensive, but you’re also getting a lower receiver that is modeled very similarly to the proven HK416 design.
- Forged from the German-made HK416
- Has a rust and corrosion resistant anodized finish
- As a stripped lower receiver, it comes ready for you to customize with additional components of your choice
- Very expensive for a stripped lower receiver
- As it’s a stripped lower receiver, it’s not ready to install with a complete upper
KE-15 Stripped Lower Receiver
The KE-15 Stripped Lower Receiver is built out of high quality 7075 aluminum with a class 2 hard coat anodized finish. This makes it durable, lightweight, and also very rust and corrosion resistant.
The KE-15 is constructed to mil-spec standards, which means that it should be compatible with all other mil-spec AR parts and upper receivers. Perhaps the best aspect of the KE-15 is the fact that it’s relatively affordable for a lower, but just take note that it’s a stripped lower so you will still need to add additional components yourself in order to transform it into a complete lower.
The KE-15 is an overall solid choice if you are seeking a forged lower receiver that is also easily affordable. This lower receiver is built out of high quality 7075 aluminum with a class 2 hard coat anodized finish, and is constructed to a mil-spec level of quality.
- Ready for you to customize
- Built to mil-spec standards
- As a stripped lower receiver, it is not yet ready to combine with a complete upper
And that concludes our list of the top three best M4 lower receivers for 2020!
Any one of the lower receivers that we have covered here today will be a solid choice for your M4, or alternatively, you can follow the buyer’s guide section that we went over earlier to help you find a good lower receiver as well.