The AR-15 has undergone many stages and several iterations in its over half a century, long active life. Based on its select-fire versions such as M16A2/A3 and the M4 service rifles, the civilian semi-automatic version of the AR-15 has become the most popular rifle for sportsmen, home defenders and firearm enthusiasts in the United States.
Whether you are shooting in a competition or plinking targets for leisure time the AR-15’s modular nature will offer you an incredible array of options for customization for an intended shooting activity.
Besides satisfaction as the primary benefit of building an AR-15, there are few other benefits of assembling two halves into one functional unit.
Comparison of the Best M16 Lower Receivers
Brownells - AR-15 M16 A1 Lower Receiver
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Brownells - AR-15 Blemished Xm16e1 Lower Receiver
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Brownells - AR-15 Blemished M16 A1 Lower Receiver
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Spikes Tactical - AR-15 Complete M4 Lower Receiver
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Aero Precision - Special Edition M16a4 Stripped Lower Receiver
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How to Choose an M16 Lower Receiver
It may be an arguable statement, but the most important things that an average AR builder wants from his lower receiver are the good fit, ergonomics, and finish.
If we neglect cast lowers as parts of doubtful value and futuristic polymer receivers of limited durability than we have to choose traditional materials and technological processes.
- When you are building an M16 on a budget, you can go with 6061-T6 aluminum since it is more than adequate in most situations but if you want the strongest and most durable material possible and the price is not an issue than the more costly 7075-T6 will be ideal solution for many firearms applications. Like one proverb says, "A little surplus never hurt anyone".
As for the manufacturing processes, we have single out billet and forged lowers.
- Solid billet lowers milled in CNC machine typically cost more than forged because of the extra machining time. These lowers usually have thicker walls for added strength. Billet receivers feature an integrated trigger guard and offer finer finish compared to the forged lowers.
- The forging process makes the receiver stronger than a cast or billet. Due to the process of forging metal, there can be slight surface imperfections like indentations. The forged lowers are lighter than their billet counterparts and are the most economic chassis for an M16 rifle.
There are three configurations available for the lowers: complete, stripped, and 80% receivers.
- Obviously, the fully completed lower assembly will help you avoid making any costly mistakes. The pre-built lower often has the lower parts kit and buffer assembly installed, making it the simplest way to build a rifle.
- Unlike complete, a stripped lower will give you an excellent price-performance ratio and tons of different styles, added ergonomic features, or ambidextrous compatibility. Being similar to a complete lower, it is considered a firearm and subject to all laws.
- Although you don’t need to be particularly mechanically inclined to put together your own rifle with custom AR-15 parts, building the 80% lowers are not for the faint of heart. However, if you have technical skills, the drilling and machining tools to assemble a 100% receiver, then jump in because this might be a project you’ll like.
Some gun owners also pay great attention to aesthetics and finish. They don't want any blemishes or defects on their lower receiver and they choose one that perfectly matches their upper receiver and the rest of the gun.
- Besides the standard anodizing (Type II) and hard-coat anodized (Type III) finishes requested by military specifications, there are few proprietary coatings providing a number of benefits including superior abrasion resistance and an extremely durable finish available in different colors.
Review of the Best M16 Lower Receivers
As mentioned in the previous section, the lowers come in various types with their own strengths and weaknesses that you should weigh.
Though it may present a challenge for an average AR owner, for this guide, we have selected mainly stripped lower receivers except one.
As a hunk of metal with holes in it, a stripped AR-15 lower does allow you to pick and choose better ambidexterity controls, built in trigger guards, "skulls and anything off of stock".
Brownells - AR-15/M16 A1 Lower Receiver
As you probably know, the original AR-15 platform has changed through the years and these improvements are marked as the different types of AR-15's. You'll often hear people refer to A1, A2, A3, or A4, but it means they are actually related to the different generations of the M16 rifle.
Historical reenactments and the increased interest of collectors for Vietnam War spawned offerings of the early AR-15 and M16A1 rifles as well as the parts kits for builders.
The Brownells is a well-known supplier for retro AR-15/M16, particularly for the AR-15/M16 A1 with manufacturer number BRN16A1. These lower receivers are immediately recognizable by the "Full Magazine Fence" typical for the third iteration in the A1 lower series.
The Brownells BRN-16A1 stripped lower receivers come from the NoDak Spud (NDS) milling shop where they start as a 7075 T6 aluminum forging. The Brownells machined them to mil-spec dimensions and finished with a matte grey or black hard anodized finish to match most of the modern uppers found on the market today.
Although this Brownells A1 retro lower is clone correct, some builders complain that it’s not as snug of a fit to the other manufacturers upper as it should be. Some people also remark that the anodizing isn't perfect as you might even come across occasional traces of residue that slightly discolor the anodizing process.
Despite sporadic complaints, NoDak Spud products are on the high end of quality and they have maybe the best reproduction lowers on the market that match the features of the original M16A1 receiver.
The BRN-16A1 Lower Receiver precisely mirrors the original form and dimensions with a proper M16A1 front take-down lug profile. Additionally, this lower fits all standard AR-15 components of upper receivers without issue.
This Brownells M16A1 lower receiver comes with engraved markings: Model: BRN-16A1 Cal: 5.56mm Mfg: Brownells Inc.
Maybe the best solution for completing your A1 Retro or Mil-Spec build is a Brownells AR-15/M16 A1 lower since this BRN-16A1 unit is an accurate reproduction of an A1 lower receiver with a fit exactly matching Brownells upper without wobble.
Best for the Money:
Brownells - AR-15 Blemished XM16E1 Lower Receiver
Since the "retro AR" scene had exploded in the last few years, many AR manufacturers, dealers and merchants have found a niche in this market.
With a renewed interest in retro guns, Brownells, in conjunction with a NoDak Spud (NDS) has brought back the M16A1 upper/lower receivers sold in sets or separately.
The forged lowers from NDS are later machined by Brownells to become the correct lower for replicas of early U.S. Army XM16E1 rifles or later released famous "XM177" Commando Carbine.
This second type lower also known as the "Partial Fence" type receiver has, unlike the first "Slabside" type, the captive pivot pins, which were held in place by a detent housed on the added reinforcement rib. This "partial fence" reinforcement is placed above the magazine release and just below the ejection port cover.
In the early stages, Brownells had a problem with one commitment segment of the AR community who preferred the original Colt XM grey finish. The Brownells receivers were excellent but too black. However, currently, they provide receivers with both grey and black hardcoat anodized finish for building reproductions of the original XM16E1.
The Brownells blemished AR-15 XM16E1 lower receivers come with the same quality forging and machining as the QC-approved receivers. In fact, they feature only aesthetic issues due to the failure in the anodizing process. The blemish units may come in varying finishes ranging from shiny green to dark grey.
This easily recognizable receiver replicates the exact contours of that "Partial Magazine Fence" configuration and offers the perfect unit for a Retro build of the first M16 rifles issued to the troops in Vietnam.
Since its founding, Brownells has been a parts company, but from 2018 they started introducing their first line of firearms. Along with Retro Rifle series which includes six "black rifles” models with prefix BRN16, Brownells released completely new “retro” components for M16A1.
The M16A1 upper and lower receivers are built from forged 7075-T6 aluminum at NoDak mill shop and then precision-machined to final dimensions by Brownells.
This AR-15/M16-A1 forged lower receiver are the ideal choice for those looking for reproduction build of a Vietnam-era type rifle because most forged lowers produced today feature incorrect "A2" profiles.
The Brownells blemished stripped lowers under manufacturer number 078-000-450WB are also often cheaper than regular ones because of small aesthetics imperfections such as discoloration and some anodizing flaws.
Besides that, few owners complained that they find the "fire & safe" markings on both sides of the receivers which is not historically accurate for an "A1" retro lower.
Although the manufacturer claims that each of their blemished M16 A1 lower receivers meets all the requirements and replicates the exact contours of the M16A1 receiver, during assembling you can expect more than the usual amount of wiggle between the two receivers, especially when pairing a lower and upper of different provenience.
Because of anodizing blemishes the finish on these lowers varies quite a bit, ranging from greenish tinted black to dull, dark grey.
While forged and machined to the same specifications as the company's full-price options, the Brownells is selling these blemished AR-15/M16A1 lower receivers at a bargain price.
The Spikes Tactical is the renowned manufacturer of complete firearms, but also they offer stripped and assembled AR-15 receivers' models.
The main selling point of Spikes M4 lower receiver is the capability to convert a regular semi-auto AR-15/M16 to selective fire gun with a drop in auto sear. It means that the Spike has lowers with a milled shelf to allow the installation of a Registered Drop In Auto Sear (RDIAS).
The complete Spikes forged AR-15 lower receiver comes with Standard Spikes Lower Parts Kit (LPK) and fire control group factory installed. Whereas most stock triggers are bad, this one is a better than average trigger.
Besides that this lower set includes a Spikes Tactical Pro Pistol grip, an M4 style six-position stock on a mil-spec buffer tube (1.146" O.D.) and a Spikes ST-T2 tungsten heavy buffer.
The M4-style adjustable buttstock and standard black pistol grip are molded from reinforced polymer to help reduce the weight, but this basic furniture isn't that great, and most AR owners change them out anyway.
Since the Spike's Tactical Complete AR-15 lower is made to the mil-spec dimensions for an optimal and precise fit, there's very little rattle or wobbling from a completed rifle using this lower. However, standard M4 carbine collapsible stock is very basic and very loose on the mil-spec buffer tube.
The lower receiver is built from a 7075-T6 aluminum forging and then hardcoat anodized in matte black finish for durability and corrosion resistance.
Whether you plan to convert your rifle to full-auto legally or you belong to those who want the novelty of the full-auto selector icon this M4 lower boasts the selector markings in the form of bullet pictograms. Without doubt, the color fill on the selector markings and the Spike’s spider logo engraving make this receiver a head turner and an eye-catching piece at the shooting range.
This guide wouldn't be complete without Aero Precision, a well-known manufacturer of mil-spec parts and accessories and one of the best makers of all-around AR-15 lower and upper receivers on the market.
While it keeps a middle ground regarding price, Aero Precision lower is the no-frills workhorse compared to other more expensive counterparts. However, it is machined from forged 7075-T6 aluminum to Mil-Spec dimensions for a perfect fit with an Aero stripped upper receiver or other AR-15/M16 standard components.
While there are no logos or markings on the right side, this well-built piece faithfully replicates the left side markings found on the actual M16A4 rifles such as "Property of the USA" and "MOD M16A4." Another added touch is the 5.56mm caliber markings and inclusion of "Safe/Semi/Burst selector markings.
Unfortunately, this black finished lower cannot be modified for full-auto mode, so the fake non-selectable "Burst" position is just for that swag.
Instead of Colt or FN logo, this stripped lower receiver features a fancy Aero Precision insignia. From an aesthetic point of view the lower engraved with distinctive Aero insignia doesn't take away from the authenticity of your build rifle, but some owners complain that they got poorly executed roll marks as it is pretty light, actually much lighter than on the Aero M4A1 lowers.
The Aero Precision Special Edition M16A4 Stripped Lower Receiver is the perfect solution for those looking for next clone build or an extremely close copy of the M16A4 currently used by the United States Military.
Types of M16 Lowers - Which is Best For Me?
In a gun community, there is a large group of AR-15/M16 builders advising to get a fully assembled upper unit and then concentrate on upgrading your lower receiver, which is pretty straightforward, compared to the upper assembly.
The market is full of various M16 lowers assemblies and lower receiver part kits, but you’ll probably need to know a few basic pieces of information about various lowers types, materials, and configurations.
Although AR-15/M16 lower receivers exist in steel and titanium iterations, they are commonly constructed from two types of materials- aluminum and polymer. Currently, most of the standard M16 lowers are machined from aluminum. There are two types of aluminum alloys of the T6 temper variety used in making AR-15/M16 receivers: 6061-T6 and 7075-T6.
One note: you can also come across the term 7071-T6 aluminum in gun literature, but there is no such thing as 7071 aluminum, and that will tell you more about that “gun writer's” competence.
The reliable 6061 aluminum was initial material in Eugene Stoner M16s, but after a few years of hard use in Vietnam War, guns receivers were starting to corrode due to the high level of moisture in the tropical environment. Subsequently, it was the main reason why the military switched from 6061-T6 to 7075-T6 aluminum and not because the 7075-T6 receivers are "stronger", as many believe.
Actually, 7075 has almost double the strength of 6061, but its hardness makes it more difficult to machine and typically it costs 2x as much as well. With better mechanical properties, the 7075-T6 aluminum alloy is the option for anyone looking for superior strength and durability.
The polymer receivers are gaining more popularity over the last few years as the next generation polymer lowers are showing relatively strong, lightweight and economical to produce. Injection molding technology has taken a great leap forward, combining high-strength resins and metal inserts added to critical areas of lowers.
AR lower receivers came in three processing methods: cast, billet and forged manufacturing methods.
Lower receivers made in the casting process have a loose crystalline structure making them the weakest and not so aesthetically pleasing to the eye. Usually, cast receivers are not recommended don't have the strength or durability to stand up to the abuse of more severe patrol work or match shooting.
Billet aluminum lowers are machined and milled from a solid block of pure aluminum on CNC machines. Since the process is so time-consuming, billet lowers tend to be more expensive than a comparable forged option. On the flipside, these rugged and good-looking lowers are inherently weaker than forged receivers are.
The forged process is the most commonly used for lower receiver manufacturing. The forging process makes the strongest aluminum form, which is very suitable for a heavy-duty M16 that you plan to use often.
The aftermarket M16 lower receivers may come in many styles and flavors with manufacturers offering assembled lower receivers, stripped lowers, or 80% lower receivers.
While the complete lowers are pretty self-explanatory, the stripped lower receiver is like the complete lower product a serialized portion of an AR-15/M16. It is also considered a firearm and it requires a NICS check or an FFL to purchase.
Though the stripped lower is just a formed piece of aluminum, many AR enthusiasts prefer building their own lower as it will offer full customization and at the same time they can save money building their lower receiver rather than buying it.
80% lower receivers are extreme since they are partly finished products (80 percent), even without holes and milling. You may not need NICS check or an FFL to build a weapon, but you will need additional tools, like a drill press or lathe and technical skills to assemble a 100% receiver.
As you might conclude from this overview, there are many possibilities to build your AR-15/M16 lower, ranging from those with blemishes to the luxurious titanium made receivers with proprietary coatings. While some lower receivers may look "cooler", and give your M16 a more refined feel, your rifle will operate the same whether they are built on a budget or exorbitantly priced receivers.
People Also Ask
According to currently adopted terminology, under the M16 term it is considered a select fire rifle and with an AR-15 name people usually recognize rifle with semi-automatic fire only. In short a word, the AR-15 is a line of self-loading weapons for regular civilian and sporting use. The M16 rifle is of a similar architecture but the military full-auto fire adaptation of the Armalite AR-15 rifle. The M4 carbine is a shorter and lighter version of the M16A2 rifle which offers distinct advantages in portability and maneuverability.
Are the Internal Parts of an M16 rifle and an AR-15 Rifle Interchangeable?
While on the outside, the M-16 and the AR-15 appear almost identical, the military fully-automatic M16s are internally different from semi-automatic AR-15s.
This means that furniture and upper receivers for the M16 are interchangeable with the AR-15, but the firing mechanisms (Fire Control Group - FCG) and some lower receivers are of a different design and they are not interchangeable.
Actually, we are talking about five major parts of the fire control group from the M-16 (trigger, disconnector/sear, hammer and fire selector) that are not interoperable in AR-15 because they are modified like a hammer and trigger assembly or disconnector, or simply an AR-15 misses certain parts like an auto sear.
Obviously, the semi-auto AR-15 models do not have three-position rotating selective fire switch like M16, but the selector switch has options only for “safe” and “fire”. However, for the collectors and re-enactors, you can find some semi-automatic AR-15 lower receivers with the words "safe", "semi" and "auto/burst" or three pictographs for the same functions.
As for the M16 buffer and BCG (Bolt Carrier Group), though they are different from those in semi-automatic rifles, both can be used in a civilian AR-15s without legality issues.
What Parts Are Interchangeable Between AR-15, M-4 and M-16?
Before answering this question, you should note that the AR-15 comes in two variants: Commercial and Mil-Spec. if your AR-15 rifle is made up to the Mil-Spec standard, its parts like buffer or buttstock will be compatible with military M16/M4 rifles
The AR-15 platform is modular, and it is assembled from three major parts: the bolt and bolt carrier, the upper receiver and the lower receiver. Except the M-4 and M-16 different designs of the hammer and trigger mechanisms, all other components are compatible and interchangeable with a semi-automatic AR-15.