Best M4 Upper Receivers – [2019 Complete Buyer’s Guide]

M4-style modern sporting rifles have taken America by storm.

Whether you are building your own rifle or replacing an old upper, there are practically endless choices for M4 uppers on the market today.

The choices can be bewildering, but we have boiled them down to a concise list of the best M4 uppers on the market today.

Comparison of the Best M4 Upper Receivers

PRODUCT DETAILS
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Brownells - AR-15 M4 Stripped Upper Receiver Black

  • Great quality, materials, and machining at an affordable price
  • Stripped down design with no forward assist or ejection port cover
  • Precision CNC machined for tight tolerances and compatibility with AR components
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Radical Firearms 16 In. 5.56 M4 Upper Assembly

  • Comes with a proprietary, easy-to-use barrel nut from Radical
  • Includes a proprietary 12-inch FCR free float rail handguard system
  • Law enforcement grade upper comes with all components and features
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Bravo Company - AR-15/M4 Flattop Upper Receiver Assembly

  • Top rail comes with laser-etched T-marks for easy return to zero
  • Complete and assembled with forwarding assist and ejection port cover
  • Professional-grade upper built for exacting specifications and tight-fitting, accurate barrel
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Spikes Tactical M4 Flat Top Upper

  • Designed and manufactured right here in the USA
  • Comes either with or without provision for a forward assist
  • CNC machining is exceptionally accurate, giving you the best fit
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PSA 16" Carbine Length 5.56 Nato 1:7 M4 Nitride

  • Includes internal components such as the charging handle and BCG
  • The bolt Carrier group is chrome-lined inside and parkerized outside
  • Thoroughly standard military design with high-grade steel and aluminum
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Are All M4 Uppers The Same?

It is true that, besides the handguard, usually you have to look closely at a selection of black rifles to see the differences, but these can be significant. Some uppers come bare and others come complete with all internal components. Some lack certain features, particularly a forward assist and a dust cover.

M4 Carbine (Source)

The forward assist is generally not as crucial today as when it was first introduced, and sometimes it can aggravate a jam, but it is nice to have. The material and finish used to produce M4 uppers are remarkably consistent, but you will see differences in fit and finish. The construction process is usually forged or billet.

Forged may be a bit stronger and heavier, but the difference is minimal. Finally, you have the option of a carry handle or flattop. The carry handle serves double-duty as an old-school rear sight. The far more common flattop design gives you a versatile rail length.

Perks of Upgrading Your M4 Upper

A new M4 upper can provide a wide array of benefits. First, older uppers eventually wear out and start to experience degraded function and reliability. A new upper can give you improved function, reliability, and accuracy at a lower cost than replacing an entire rifle.

Perhaps there is a function lacking on your old upper that you have always wanted. Whether that is a different style or length of rail, a forward assist, more ergonomic controls, or even a new caliber, you can get it with a new upper. The modularity of the M4 design even allows you to run different uppers in different situations.

They are fast and easy to switch out. Sometimes, we have the money and taste to replace an upper strictly for aesthetic reasons. There is a wide variety of colors, finishes, and styles available.

Aspects to Consider Before Buying

The first thing to consider in firearms components is reliability. M4 uppers also offer different levels of fit and finish, which can affect accuracy. The best way to ensure you get the most reliable and accurate product is to go with a well-established company and a proven model.

Brownells - AR-15 M4 Stripped Upper Receiver Black 

Getting the best reliability at an affordable price can be a challenge, but that's what we are here for. The main choice is between bare and complete uppers. If you want to select every internal component of your rifle, go with the former.

In terms of material and finish, there is a 99% chance that you are going to get an upper made of 7075-T aluminum alloy with a black, mil-spec, hard coat finish. Billet uppers offer more aesthetic options than forged ones. Forged uppers are arguably stronger, but the difference is going to be minimal. Some come with extra coatings like Teflon or chrome-lining to increase function and durability.

Quick Take - The Best M4 Upper Receivers

Review of the Best M4 Upper Receivers

With so much to think about, you could spend a lifetime sifting through the options. Luckily, we have put in the time, so you don't have to. Here is our guide to the best M4 uppers on the market now.

Pros

  • Excellent Quality, Materials, and Machining at a Great Price
  • Stripped Down Configuration With No Forward Assist or Ejection Port Cover
  • CNC-Machined for Precise Tolerances and Compatibility with AR Components

Cons

  • Dust Covers May Not Fit Perfectly

Brownells is one of the nation's largest firearm and firearm component distributors. As such, they have a wealth of data on what shooters want, what works, and what works reliably. They use this valuable knowledge to produce many of their own affordable, yet high-quality products.

With this stripped upper receiver, Brownells offers a basic, no frills but top-quality item to build your own custom M4 around. Brownells has used a 7075-T6 aluminum alloy for this upper, the standard with most modern sporting rifle receivers. This flattop upper is forged and then CNC-machined to precise tolerances, making it compatible with the vast range of nominally mil-spec AR components.

It has a matte black, type-III, hard coat anodized finish. Brownells has included a few nice little features like pivot/takedown holes and a T-marked Picatinny top rail. Of course, this product has M4 feed ramps for the most reliable feeding. This upper is as minimalist as they come, with no forward assist or ejection port cover. It is entirely made in the U.S.A.

​Bottom Line

This is an excellent option if you are a tinkerer and want to build your own simple, lightweight upper. The top features are the T-marked rail, the overall simplicity, and standard, mil-spec dimensions. This is an excellent, no-brainer option from a great manufacturer. Plus, it's always nice to buy domestic products.

Pros

  • Includes a Proprietary, Easy-to-Use Barrel Nut From Radical
  • Comes With a Proprietary 12-Inch FCR Free-Float Rail Handguard System
  • This Law Enforcement-Grade Upper Comes With All Components and Features Needed for Drop-In Use

Cons

  • Occasional Lapses in Quality Control and Customer Service

Radical Firearms is a Texas company that started out small but has carved out a nice niche for itself in the market. Their success comes on the back of quality manufacturing covered by a lifetime warranty. This is a complete mil-spec upper in a 16-inch SOCOM configuration.

This is great for any shooter, novice or advanced, who wants to drop a complete upper into their lower receiver and start shooting with minimum fuss. One top feature of this upper receiver is Radical's proprietary 12-inch FCR free-float rail handguard system. This gives you the best accuracy while keeping barrel heat away from your hand, thanks to the M-Lok thin rail.

The barrel is made of 4140 Chrome Moly Vanadium finished in Melonite. It has a 1:7 twist rate. An A2 flash hider sits at the end. As usual, the upper itself is made of 7075-T6 forged aluminum alloy, finished with type-III anodizing. The bolt carrier group is finished in nitride. The barrel nut is a proprietary, easy-to-use Radical design. This upper comes with a forward assist and an ejection port door.

Bottom Line

If you need a great quality, yet affordable, upper that you can drop into your existing lower and start shooting right away, this is the option for you. The top features are Radical's proprietary free-float handrail and barrel nut.

Pros

  • Complete and Assembled, Including a Forward Assist and Ejection Port Cover
  • The Top Rail Comes With Laser-Etched T-Marks so Sights Can Easily Be Returned to Zero
  • This Professional-Grade Upper is Built to Exacting Specifications and Features a Tight-Fitting, Accurate Barrel

Cons

  • The Barrel Mounting May Not Be an Ideal Fit

This is another professional-grade upper from one of the most respected names in the modern sporting rifle field. Bravo Company is owned and run by veterans and ex-special forces personnel. They develop weapons systems based on their own combat experience and exacting demands.

This upper is constructed to exacting military standards. One exception is that the inside diameter for the barrel extension is very slightly undersized to provide a tight fit and ensure a more accurate rifle. The top rail features laser T-markings so that sights or other components can be quickly and easily returned to zero. This upper is CNC-machined from type-II, anodized 7075-T6 aluminum alloy to provide more than enough strength.

It comes assembled with a forward assist and an ejection port cover. The forward assist has a heat-treated, tool-steel pawl, featuring press fit and a pinned cap. The interior bore has a dry film lubricant in accordance with military specifications. This is an excellent upper built to exacting standards and offered at a decent price. Rarely do you hear a bad word said about Bravo Company.

Bottom Line

This is a great, high-quality upper. The top features are the result of careful machining and tight tolerances. The barrel fit can be a challenge but will be worth it in improved accuracy.

Pros

  • Engineered and Produced Right Here in the U.S.A.
  • The CNC Machining is Exceptionally Precise, Giving You the Best Possible Fit
  • Available Either With or Without Provision for a Forward Assist and Ejection Port Door

Cons

  • Ships Without Enough Padding to Prevent Cosmetic Knicks

Spikes Tactical is a family-run company out of Florida. All of their products are made in the U.S.A.and are covered by a lifetime warranty. This dandy little upper comes either with or without a forward assist. You will have to decide for yourself whether it is necessary.

Advances in M4 design since the introduction of the forward assist arguably render the feature unnecessary. Some say it can even exacerbate a jam. Others call it a life-saver. The option with the forward assist also includes an ejection port door.

This flattop upper has a standard M4 Picatinny rail. It is CNC-machined from 7075-T6 aluminum alloy and finished with a black, type-III, hard coat anodization. This is a top-quality, carefully machined upper that offers a high level of shooter satisfaction.

Fit and finish are outstanding. The simpler version without provision for a forward assist or ejection port door weighs 5.9 ounces and the one with the forward assist weighs 8.5 ounces. Both versions are stripped down, giving you the opportunity to select your internal components separately.

Bottom Line

This is a great quality, stripped-down upper receiver. Whether you want a forward assist or are going for that sleek, stripped-down look, you can't beat this option. The top features of this upper are the layout options and the precise machining.

Pros

  • M4-Style Feed Ramps
  • Familiar, Thoroughly Mil-Spec Design Using Only Top-Quality Alloys
  • Includes All Necessary Internal Components Such as the Bolt Carrier Group and Charging Handle

Cons

  • Buyers May Experience Quality Control Issues, Especially With the Finish

This is a classic, mid-20th-Century-style M4 upper made by PSA. If you need a quick and easy option for an upper to switch out an old one, this is a solid option. It comes with a standard 16-inch, A2-style barrel made of 4150V Chrome Moly vanadium steel.

The barrel is finished with a high-quality nitride and features a twist rate of 1:7 inches. This twist rate is great for most bullet weights. The barrel is also treated with melonite to increase its dependability and accuracy. All the features of the barrel are true to the A2-style, including the flash hider and the F-marked front sight base.

The sight base also comes with a handy swivel. The handguard is the mid-20th-Century-style A2 design without any lengths of rail. The gas system on this PSA upper receiver is mid-length. The receiver body itself is forged for strength.

Inside, there are M4 feed ramps and an M16 bolt carrier group. The external surface of the BCG is parkerized and the inside surfaces are chrome-lined for great reliability. The BCG is produced from top-grade, mil-spec, shot-peened Carpenter 158 tool steel. A charging handle also comes standard with this complete upper. It is completely designed and made here in the U.S.A.

Bottom Line

Whether you want a new, reliable, and solid quality M4 upper or you want to stick with that mid-20th-Century military look, this model is an excellent choice. All of the design details and construction methods are based on decades of military feedback.

The best features of this upper are the quality of the materials, alloys, and metal finish. As a complete upper, this unit is a perfect choice for anyone that isn't interested in tinkering around choosing their own internal components.

Conclusion

Now you know what the best M4 uppers out there are. Everyone has their own preferences, but we're sure that, whatever you are looking for, you will find it in our list. In fact, why settle for one M4 upper? Follow our other guides to experiment with using uppers in upgraded, non-standard calibers.

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