Best AR 15 Upper Receiver Assemblies You Should Own

Disclosure: Some of the links below are affiliate links, meaning at no additional cost to you, Ammoland will earn a commission if you click through and make a purchase.

By just by pushing out two little pins, slapping on a new AR 15 upper receiver assembly, one gun can become many guns.

FNH USA makes multiple AR 15 Upper Receiver Assemblies

USA--( AR-15 rifles are modular.

Push out the take-down and pivot pins and remove the AR 15 upper receiver – it contains the barrel and the matching bolt carrier group, the charging handle, and the gas system.

If you’ve zeroed an optic or scope, it comes with the AR 15 upper receiver, too. Replace the original upper assembly with a different one; push the two pins back into place, and voila! You’ve got a different gun.

Standard 5.56mm lowers can’t accept larger .308 uppers, and vice versa. But there are plenty of uppers in all sorts of calibers that will work perfectly with standard 5.56 lowers, and the lineup seems to expand all the time.

There are many complete AR 15 upper receiver assemblies available that are literally “plug and play” on any standard AR lower assembly.

And if you’re comfortable with a few basic tools – like a vise and a barrel nut wrench – you can easily build up your own stable of extra AR-15 complete upper assemblies. Quality suppliers like Brownells have all the barrels, uppers, handguards, bolt carrier groups, and associated tools you’d need.

Why would anyone go to the trouble of getting a bunch of uppers to go on just one AR-15 lower?

Think of it this way. You’ve spent time and money getting exactly the trigger you want, and the best stock that fits you perfectly. Maybe you’ve added a Magpul BAD lever, and the ideal pistol grip for your hand. Why should you give all that up just because you want to do a different kind of shooting, at a different distance?

The good news is that you don’t have to, at least not if you get a spare complete AR 15 upper receiver assembly… or three. That way, you can use the same gun for everything from plinking soda cans on the family farm, to sniping steel targets way out there, to hammering feral hogs in thick brush, just by pushing two pins and swapping uppers.

I’ve put together a list of complete upper assemblies every Black Rifle owner should consider. I’m basing this list on the assumption that you’ve already got an AR-15, most likely a 16-inch carbine in 5.56, but don’t worry I have added a suggestion for one of those as well.

And if you don’t yet, now is the time to buy, as there are tons of top quality rifles out there.

But here’s my list of the Best 5 AR 15 Upper Receiver every Black Rifle shooter should think about owning.:

#6 – 5.56 AR 15 Upper Receiver Assembly:

Aero Precision M4E1 Assembled Upper Receiver 18" 5.56 Rifle Length
Aero Precision M4E1 Assembled Upper Receiver 18″ 5.56 – Rifle Length

To start we are talking about the go-to product of AR15 upper receivers. The 5.56/.223 rem complete upper receiver.

Most of the folks reading this will already have an upper receiver in 5.56 or .223 that came with the purchase of your basic rifle package. But If you are building a rifle from scratch a rock-solid proven upper is the Aero Precision M4E1 Assembled Upper Receiver 18″ in 5.56.

The M4E1 5.56mm 18″ Rifle Upper Receiver adds two important benefits to Aero Precision’s M4E1 carbine upper. First, the longer 18″ barrel imparts extra velocity to the bullet with a very small addition to the rifle’s OAL. Second, the longer rifle-length gas system slows down gas velocity for gentler cycling that leads to improved reliability and reduced wear on moving parts and the receiver. The result? Rifle-like performance – and versatility – in a carbine-sized package.

The Aero Precision M4E1 5.56mm 18″ Rifle Upper Receiver delivers all the other benefits of Aero’s M4E1 receiver line. The bolt/carrier group and charging handle are omitted so you can customize those parts to suit your needs. (Why pay for parts you’re only going to replace anyway?) The forged M4E1 receiver has the unique appearance of a custom “billet” receiver, yet accepts standard AR-15 “mil-spec” parts.

We can not recommend this upper enough.


#5 – A Big Bore AR 15 Upper Receiver Assembly:

Alexander Arms U-BEOOM .50 Beowulf Complete Upper Assembly
Alexander Arms U-BEOOM .50 Beowulf Complete AR 15 upper receiver Assembly

As good as the 5.56 cartridge is, there are some things it just doesn’t do that well. Like delivering whomper-stomper hits on big, tough game animals like feral hogs. There are several different big bore cartridges out there designed to fit through an AR-15 magwell, and it seems like more are developed by creative wildcatters every year.

50 Beowulf Ammunition
50 Beowulf Ammunition

Some of the really popular big-bore AR cartridges include .450 Bushmaster, .458 SOCOM, and .50 Beowulf. All of them throw big fat bullets at relatively slow velocities and are devastating at close range. If you want readily available factory ammo, .450 Bushmaster might be the best bet. If you handload, .458 SOCOM probably gives you the most versatility, as it uses rifle bullets available in a wide range of weights and styles – as heavy as 600 grains if you want.

And if you really must have a caliber that starts with a 5, and is named after an epic hero, then .50 Beowulf is the only choice. Direct from the creator of the Beowulf round is the Alexander Arms U-BEOOM .50 Beowulf Complete Upper Assembly.

Perhaps the best aspect of adding a Big Bore AR 15 upper receiver is that you can typically use standard 5.56 magazines, although Bushmaster does add a special “single stack” follower and springs to standard 20-rd magazines specifically for use with .450 Bushmaster ammo. Any of these cartridges will give your AR-15 performance similar to the venerated 45-70 at close range, in a lightweight, semi-auto package. The possibilities are endless.

If you decide to build your own Big Bore AR 15 upper receiver assembly, be sure to either enlarge the ejection port, or get an upper with an ejection port specially made to accommodate the big fat cartridge cases.


#4 – A 6.5 Grendel AR 15 Upper Receiver

Alexander Arms U-65-18 SCHUNT 6.5 Grendel 18" Side-Charging Hunter Upper
Alexander Arms U-65-18 SCHUNT 6.5 Grendel 18″ Side-Charging Hunter Upper

The 6.5 Grendel is an amazing cartridge. It uses 6.5mm bullets, known for having good sectional density and relatively high ballistic coefficients – which means they fly very well, even in stiff crosswinds. The Grendel gives performance similar to, if not better in some ways as the .308, but in a cartridge that can fit inside a standard AR-15 lower.

6.5 Grendel Ammunition
6.5 Grendel Ammunition

Several years ago the 6.5 Grendel’s creator, Bill Alexander, opened the door for even more manufacturers to crank out ammo, parts, and barrels with the name “Grendel” on them. Not surprisingly, Alexander also first developed the .50 Beowulf, and took the Grendel’s name from the same Old English saga.

Unlike the Big Bore AR 15 upper receiver, a 6.5 Grendel will require a magazine, like the C-Products Ar-15 / M16 6.5 Grendel Mag, specially shaped for that round.

For reaching way out there with a standard-sized AR-15, it’s hard to beat the 6.5 Grendel. Be sure to add a good-quality scope and some nice rings to complete the package.


#3 – 300 AAC Blackout AR 15 Upper Receiver.

HIGH STANDARD AR-15 Complete 300AAC AR Upper Receiver
HIGH STANDARD AR-15 Complete 300AAC AR Upper Receiver

The 300 AAC Blackout cartridge gives performance very similar to the 7.62×39, but in a cartridge that works perfectly with standard AR-15 bolts, magazines, and lowers. You can convert any standard 5.56 AR-15 to .300 AAC Blackout by merely changing only the barrel. Of course, if you don’t want to mess with taking apart your current AR 15 upper receiver, you can just drop a complete 300 AAC Blackout upper. like the Aero Precision M4E1 Threaded 16″ .300 Blackout Complete Upper Receiver with the ATLAS S-ONE Handguard, onto your lower.

300AAC Blackout Supersonic Elite Performance Ammunition
300AAC Blackout Supersonic Elite Performance Ammunition

Why not go with an AR-15 upper in 7.62×39 in the first place?

You can use less-expensive steel-cased ammo in a 7.62×39, but there are tradeoffs. Typically, you’ll also need to put in an extra-power hammer spring to help reliably ignite the sometimes-harder primers found on cheap, foreign-made steel cased ammo. Many shooters also add in special firing pinsto help set off primers in less-expensive steel cased ammo.

Finally, you must have specially-shaped mags for a 7.62×39 AR. But the 300 AAC Blackout uses the standard 5.56 mags that you probably already have in good supply.

Where the 300 AAC Blackout really shines is with sub-sonic loads combined with a suppressor. Suppressed, it is remarkably quiet, has little recoil, but still lets you thump targets with bullets that weigh up to 220 grains.

If you live in a state that allows suppressor ownership, you really should consider getting an AR 15 upper receiver in .300 AAC Blackout with a suppressor-ready muzzle device, like SilencerCo ASR 5.56 Muzzle Break.


#2 – 22 LR AR 15 Upper Receiver

Tactical Solutions AR-15 .22LR M4 & Lightweight Upper Receivers
Tactical Solutions AR-15 .22LR M4 & Lightweight Upper Receivers

Yes, I know we’re still in a .22 LR drought, but there seem to be signs of it easing. Maybe. Even with .22 LR hard to come by in some locales, a dedicated .22 LR upper makes a lot of sense for AR-15 owners.

You can get conversion kits that let you shoot .22 LR through any standard 5.56 AR-15, just by swapping out the bolt and carrier group and using a special magazine. And these kits are almost always less expensive compared to dedicated .22 LR AR 15 upper receiver. Many shooters get these kits and enjoy them a lot. But there are some reasons why you might want to consider a dedicated .22 LR upper.

.22LR Ammunition
.22LR Ammunition

First, dedicated .22 LR uppers, like Nordic Components 22RB Dedicated 22 Upper Receiver, typically have barrels specifically rifled to work with slower, lighter, all-lead projectiles fired from rimfire cartridges – something like a 1-16 twist. The twist rate in your 5.56 AR-15’s barrel is intended for 55 grain, or heavier, jacketed bullets moving at much faster speeds. The slower twist rate often results in better accuracy from a dedicated .22 LR upper compared to a conversion kit.

Second, true .22 LR uppers are blowback, and don’t need a gas block or gas tube, and are thus often lighter. With a standard conversion kit your 5.56 AR still wears its gas block and gas system parts when you swap out just a bolt carrier group and magazine to convert to .22 LR.

More accurate and lighter easily translate into more fun, which are both important, especially if you’re using your .22 LR AR 15 upper receiver to help introduce young or new shooters to the game.


#1 – A Varmint or Precision AR 15 Upper Receiver in .223/5.56

DPMS Upper Receiver .223 cal 16" Bull Barrel Parkerized
DPMS Upper Receiver .223 cal 16″ Bull Barrel Parkerized

Let’s say you have a 16-inch AR carbine, and you’ve carefully selected the stock, trigger, and pistol grip that suit you best. You aren’t interested in having to worry about another caliber, but would like to be able to reach out a little farther and a little more precisely.

HPR .223 Remington Ammo
HPR .223 Remington Ammo

Your best bet might be to invest in a dedicated varmint or precision upper, especially one with a high-quality scope mounted.

Here’s how that combination could work. The 16-inch carbine upper is lightweight and fast handling, especially if you put a red dot or similar electronic sight atop it. With that rig, you can get quick hits inside of 300-yards, exactly what you need for self-defense, many types of action shooting sports, and certain types of hunting.

But what if you could convert the same gun into a tack driver in less than 60 seconds, and then smack small targets and varmints, out to 500 yards, or maybe even further? If you’ve got an AR-15 upper receiver, like the Daniel Defense MK12 Upper Receiver Group then add a bipod, long-range scope and you can – provided you develop your shooting skills enough.

It’s an idea that even the US military likes, with the various versions of the “DMR,” or Mk 12 Special Purpose Rifle sharing several of those features.

Of course, just slapping a free-float, heavy-barrel upper onto your carbine lower will not magically transform it into a Mk 12 SPR, but it can give you some real upgrades when it comes to longer-range performance.

New Take On Old Saw

There’s an old cliché out there that goes something like this, “Beware the man with only one gun. He probably knows how to use it.” But if that “one gun” is an AR-15, it can quickly turn into a whole lot of different guns, just by pushing out two little pins, slapping on a new AR 15 upper receiver assembly, and pushing those two little pins back into place.

Thomas Conroy is a firearms aficionado and writer who lives in the Midwest.

Add Comment

Your email address will not be published. Required fields are marked *