Arguably one of the most vital elements of the AR-15 is picking the right upper receiver group. After all, your upper provides the lock-up between the bolt and barrel, leaving you with either an accurate and dependable firearm or something that offers little more than consistent frustration.
If you want to build an AR for precision shooting, general use, or home defense/close-quarters combat, there’s an upper out there for you, but how do you go about picking the best one?
Comparison of the Best AR-15 Upper Receivers
|Complete - Best Value: PSA Mid-Length 5.56 NATO Upper|
|Complete - Best 16" Upper: Aero Precision Upper Receiver|
|Best Assembly: Bravo Company Flattop|
|Most Customizable: Centurion Arms RECCE|
|Complete - Premium Upper: Daniel Defense DDM4V7 Upper|
|Complete - Best Short Barrel: Geissele Super Duty|
|Complete - Best Lightweight: KAC Precision Upper|
|Also Great: LaRue Ultimate Upper Kit|
|Best Alternate Caliber Upper: Noveske Gen 3 Upper|
|Also Great: SOLGW 5.56 NATO Lightweight Upper|
What to Look for in a Quality AR Upper
Key in the functionality of Eugene Stoner’s AR-10/AR-15 design, now pushing 70 years young, is the fact that it utilizes a two-piece receiver consisting of an upper and lower element.
The complete upper typically consists of the receiver itself, the barrel, gas system, flash hider, front sight assembly, rail system/handguards, slip ring, ejection port/dust cover, charging handle, bolt carrier group, and forward assist assembly on M4 style carbines.
Lowers, on the other hand, house the trigger assembly, mag well & release, bolt catch, grip, and a whole universe of springs and pins (which can generally be purchased as a single lower parts kit, or LPK.)
1. Grade of Aluminum
Uppers are almost always made from aircraft-grade aluminum (dating back to Stoner’s original work with the Fairchild Aviation-owned ArmaLite Rifle Company) and typically come in two grades, 6061-T651 and 7075-T651, with the latter being preferred as it is near twice as strong when it comes to tensile and yield strength for very little difference in weight.
2. Billet or Forged
Uppers can be either forged or billet construction, with the first typically being more common (and affordable) and the latter largely in the realm of more custom builds as it has more machining steps to finish.
3. Barrel Length
AR-style rifles and pistols are truly modular, enabling the user of one to quickly swap out compatible upper and lower receivers in minutes with little or no tools and completely change the traits of the firearm.
With that, complete ARs, ready to fire right out of the box once function-checked and loaded, can be bought and used then later easily upgraded by swapping out the upper.
The modularity of the AR platform allows for an AR owner to have a single lower– typically the only serialized and controlled part– that will fit an entire shelf of widely different uppers, each with a separate purpose.
Likewise, uppers can generally be swapped across several lowers, one of the reasons why ARs are sometimes referred to as “Legos for adults.”
Taking it a step further, home builders/assemblers can start simply with a stand-alone lower receiver and add their selected AR-15 complete upper receiver of choice.
Does an AR upper require an FFL or other ATF red tape?
To stay legal and in compliance with the National Firearms Act, rifles must have a minimum barrel length of at least 16-inches. Many manufacturers bill their carbines as having 16.1 or 16.5-inch barrels just to have a skosh of extra insurance to keep ATF screeching harmlessly from the trees.
There is, however, a tendency from some AR makers to market uppers and all-up carbines with 14.5-inch barrels targeting the M4 upper/home defense arena but with a permanently attached muzzle device or barrel extension to make up the difference and reach that 16-inch threshold.
SBRs & ATF Forms
If you want to go shorter than that, you can get an NFA-registered short-barreled rifle (SBR) AR, either outright through a Form 4 or make one with an approved Form 1, or settle for an AR pistol which has its tradeoffs.
Be incredibly careful when it comes to having a pistol-length AR upper and an AR carbine/rifle lower without a stamp and proper paperwork. See “constructive possession” for more info on that as we are not lawyers and none of this constitutes legal advice (we are, after all, just monkeys randomly pounding keys on a keyboard).
Understanding the laws and implications of owning or building a firearm is always 100% your responsibility.
4. Stripped or complete
Going back to the modularity built into the AR series, upper receivers can be purchased anywhere from bone stock basic– with *only* the one-piece “stripped” aluminum receiver– up to being complete and ready to install on a lower before heading to the field or the range.
For those looking to go stripped, that option can be attractive for fully custom guns in which each part and component is carefully selected – be it for purpose, weight, or cost – mil-spec or otherwise – and used to assemble an AR-15 upper to spec.
For those looking for a more plug-and-play option, a complete upper is the way to go as they often just require sights or an optic and marrying to a lower to be range-ready.
Further, due to the economy of scale and resulting deep discounts that gun makers get on bulk parts, complete uppers are usually cheaper than if you were to part out each component, making them a great deal in many cases.
5. Upper Style
When shopping for upper receivers, keep in mind that there are four recognized generations; A1, A2, A3, or A4.
“Old school” A1 and A2 uppers
The original “old school” A1 and A2 uppers have an integral carry handle at the top (12 o’clock) position of the receiver that includes the rear sight assembly.
Other than the sights, the primary difference between the two, when found in a complete receiver, is that an A1 will have Vietnam-style triangular handguards with a “sawtooth” ridge on top while the A2 will typically have rounded thermoset handguards.
Going even more throwback, Brownells has been marketing retro AR uppers and rifles with a slick-sided pre-A1 setup lacking a forward assist and brass deflector on the receiver.
A3 and A4 upper receivers
Modern commercial A3 and A4 upper receivers are much more functional, replacing the carry handle with a flat top Picatinny rail for sights and optics– or even a removable carry handle if that is your thing.
The difference between the two is that the A4 has M4-style extended feed ramps, which are better when it comes to reliability. These days, except for DCM style full-length uppers, most current A3s and A4s use a free-floating handguard with some sort of accessory slot or rail system.
6. Gas system or piston
Stoner designed the AR-15 platform to utilize a direct impingement gas system to cycle the action and all this magic takes place within the upper receiver.
The concept is straightforward – bleeding off a portion of the spent gas from the fired cartridge through a small port in the barrel to a gas block and from there back to the bolt carrier’s gas key along a gas tube that runs atop the barrel, working the bolt.
This method is reliable, is standard for most uppers and builds, and has been in service for generations. However, it is also kinda dirty, as it throws burnt propellant gasses and bullet particles back into the action, in effect fouling the system a little bit with every shot.
The basic operation of a classic Stoner-engineered AR direct impingement gas system
Piston guns, substituting a short gas piston and operating rod at the gas block for the gas tube and gas key of Stoner’s original design, are a newer trend in the AR world.
On the upside, since the op rod cycles the bolt into the receiver, less hot gasses, and particulates are pushed into the chamber, leaving a cleaner gun which tends to be more reliable in operation, especially when used extensively without cleaning.
On the downside, piston AR uppers are more expensive and require a piston-specific bolt carrier group to work, limiting the choices on BCGs for those who select to drop the gas.
A piston-based AR upper is cleaner and more reliable, but more expensive and requires a piston-specific BCG.
7. Gas system length
With AR-15 barrels running from carbine-length 16-inch to 24-inches for precision rifles and down to 6-inches on pistols, there’s a huge number of variables at play – all with specialized gas systems, different gas port sizes, and tube lengths to make each gun run.
Rifle, Mid, or Pistol Length?
For instance, Rifle-length systems, for barrels 20-inches and up, typically have a .093-inch port and companion gas block 12 inches down the length of the barrel.
Mid-length systems run 14- to 20-inches in barrel length with a .0625-inch or larger port 9-inches down the barrel. Carbine length, 10-to-18-inch/.070/7-inch. And pistol length for those under 10-inches with a .070-inch port at least 4-inches down the barrel.
Of course, gas port size varies by the manufacturer as each tries to chase down the double-edged sword of consistent reliability without wickedly over-gassing a rifle, but that’s a subject for another day…
For general purposes, mid-length gas systems are preferable for most uses as they have a healthy dwell time and lower gas port pressure while providing ample handguard accessory slot real estate and a decent sight radius.
When it comes to wringing the most out of the round, especially when using heavy bullets such as 77-grain loads in 5.56, the rifle-length system is ideal offering softer felt recoil with the chunkier rounds.
The shorter you go – into the carbine, pistol, or hybrid dissipator lengths – the more you start shedding performance while simultaneously ramping up a more rowdy – and less reliable – shooting experience. These factors cause many to set these systems aside as more range toys than functional platforms, at least where 5.56 NATO is concerned.
The Best AR-15 Upper Receivers Reviewed
1. Palmetto State Armory (Best Value)
Sometimes derided for the fact that they are the master of the low-cost AR, Palmetto State Armory has truly revolutionized the black rifle market in the past decade, offering a respectable product at an exceedingly fair price coupled with a deep supply chain that ensures they are almost always in stock– a rarity in strange times such as these.
One of their best deals is on their 16-inch PSA M4 5.56 NATO carbine uppers, available in either a 1:7 or 1:8 twist. These come standard with a Magpul MOE handguard and 4150V chrome moly vanadium barrels. Further, they come complete with at least some sights– Magpul MBUS– and with a full-auto profile BCG included all for typically well under $500.
2. Aero Precision (Best 16" Upper)
With offerings that include stripped, complete and enhanced uppers of all stripes, Aero has something for every AR builder. One of their best deals consistently is on their M4E1 Enhanced upper which has a novel way of securing a free-floated handguard and comes complete with M4 feed ramps and T-marks.
3. Bravo Company Manufacturing (Best Assembly)
BCM has dozens of upper receiver groups running from short 9- and 10.5-inch pistol uppers to 20-inch rifle models in a variety of calibers. About the most-feature rich of these is their Kyle Defoor KD4 series uppers with SS410 barrels, ideal for use with 77-grain pills.
4. Centurian Arms (Most Customizable)
Based on the Recon rifles built for Naval Special Warfare operators, Centurion has been offering models of their RECCE model uppers in either 14.5- or 16-inch barrel lengths for years and it is easy to see why when you look at them.
These things are tight, and the company has a range of customizable options that leaves the buyer with exactly what they want.
5. Daniel Defense (Premium 16" Upper)
Georgia-based Daniel Defense is a staple in the quality-built AR world and their upper game is on point, offering over 20 complete receivers in both .300 BLK and 5.56 NATO.
Of these, their MK12, which uses the USSOCOM-spec low-profile MK12 gas block on a soft-shooting rifle-length gas system coupled to an 18-inch stainless barrel, is no slouch.
6. Geissele Automatics (Best Short Barrel Upper)
Based in the Keystone State, Geissele is a well-known player in the AR upper department and their Super Duty models are respected.
Moving past the SDs, which can sometimes be hard to find, the company’s URGI is about as bombproof as it gets, outfitted with all the Geissele bells and whistles from its Super Modular Rail MK 16 handguard to its Airborne charging handle and Super .750 gas block.
7. Knights Armament (Best Lightweight)
Florida-based Knights Armament was significant in the AR world as the last home of Eugene Stoner and they benefited from the famed inventor’s most advanced ideas on the platform.
The company’s upper catalog has several pages with the SR-15 E3 Mod series being one of the most appealing, offering a light 4.3-pound kit with a 1:7 twist barrel, everlasting round-lug bolt, and M-LOK free-floating handguard.
8. LaRue Tactical (Also Great)
With a name like the “Ultimate” upper, it would seem that Texas-based LaRue is doing a bit of smack talking but it just seems that way.
Offered in four caliber choices including 6.5 Grendel and .224 Valkyrie, the Ultimate includes Stealth 2.0 M-LOK handguards, M4 feed ramps, LaRue’s TranQuilo muzzle brake, an MBT two-stage trigger (to fix up your lower), and barrel lengths from 12- to 20-inches.
9. Noveske (Best Alternate Caliber Uppers)
Noveske isn’t shy about their guns or black rifle components and has always been one of the loudest voices in the AR community, but you can’t fault them on the quality of their products. When it comes to uppers, they have a full selection with the 14.5-inch Gen III Afghan being our personal favorite.
Shipping standard with a stainless 1:7 barrel with a mid-length gas system, NSR M-LOK rail, Geissele Super Badass charging handle, and Dead Air muzzle device, they offer a choice between a polygonal twist or CHF chrome-lined barrel. About the only bad thing we can say about Noveske is the price– we don’t think you can find one of their uppers for an MSRP of less than four-digits, without a decimal point.
10. Sons of Liberty (Also Great)
Texas-based Sons of Liberty Gun Works doesn’t mess around when it comes to their product line and their upper receiver groups are good-to-go and rugged, meant for hard work.
One of the sweetest of the pack is their M4C4 Patrol upper that comes standard with a Centurion C4 quad rail– an item you don’t see a lot of these days– and a Liberty Fighting trigger.
- Reddit, Guns are just Legos for adults
- Bravo Company USA, BCM AR15 Kyle Defoor KD4 Upper Receiver Groups
- NRA-ILA, National Firearms Act (NFA)
- Bureau of Alcohol, Tobacco, Firearms, and Explosives, National Firearms Act
- Stroleny Law, P.A., Gun Possession: Actual and Constructive
- Bureau of Alcohol, Tobacco, Firearms, and Explosives, Form 4 – Application for Tax Paid Transfer and Registration of Firearm (ATF Form 5320.4)
- Wikipedia, Infinite monkey theorem
- Bureau of Alcohol, Tobacco, Firearms, and Explosives, Application to Make and Register a Firearm
- Metal Supermarkets, What are the Differences Between 6061 and 7075 Aluminum?
- YouTube, How An AR-15 Rifle Works: Part 2, Function
- YouTube, Adams Arms Piston System Animation
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