Best Sig MCX Uppers of 2022 – Ultimate Review

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The Sig Sauer MCX is a formidable, effective and widely appreciated weapon with a compact design.

The modular design of the MCX gives you a chance to club it with the famous AR lower platform to switch between both these amazing rifles almost instantaneously. 

Here we will take a peek inside the world of Sig Sauer MCX upper receivers, and how buying one can be a smart move on your part. So keep those eyes pinned on the screen. 

Comparison of the Best Sig MCX Uppers

  • 5.56 MCX conversion upper with a 16 inch barrel
  • Full length top rail, m-lok compatible handguard with QD sling points
  • Intricate design with smartly created cuts for reduction in overall weight
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  • 300blk conversion upper with suppressor can for noise reduction
  • Includes adapter for compatibility and a two stage factory trigger
  • Pinned and welded suppressor doesn't convert your rifle to an SBR
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  • Best MCX rattler conversion kit combo for 300blk caliber
  • Combo includes a trigger, adapter and the receiver with full length rail
  • Compact design with a 5.5 inch barrel and handguard with QD sling point
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Can You Really Find a Quality MCX Upper That’s Affordable? 

Well, the question itself is quite comprehensive and the answer is equally subjective. When you are talking about a Sig Sauer MCX, ‘cheap’ is not the word you should use. However, ‘affordable’ is a relative term for every individual depending upon how much money you can spend. 

There’s really no trade-off between quality and price when a MCX upper is concerned. While the rifle itself is priced above $1,900 with almost every online and offline supplier. Affordability doesn’t really present itself as a question. 

Additionally, since all these parts are indigenously manufactured only by Sig Sauer, the company has a monopoly on the price. Although it also means that all the aftermarket uppers are OEM and feature the best quality. 

Sig MCX in use. (Source)

How Do I Choose a Sig MCX Upper?

Choosing an MCX upper is similar to choosing the upper receiver for an AR, or any other comparable rifle for that matter. Here are certain things you should consider when choosing a receiver.

Compatibility - Adapter and Trigger

If you are buying a Sig MCX Upper, it is almost obvious that you are planning on coupling it with a standard AR receiver. Before you do that, please be aware that these uppers require a special adapter and trigger upgrade to function with standard AR style lower receivers.

Quality and Finish

Make sure that the quality and finish of the upper receiver casing, bcg, barrel and handguard adhere to the highest standards. There are quite a few different MCX versions available on the market which feature different barrel lengths, gas systems and finish. So you can choose one that suits you the best. 

MCX 5.56MM NATO AR Conversion Upper

Complete or Unfinished 

You can either buy a complete MCX upper receiver or assemble different parts for more customization. However, buying a complete receiver saves you from the hassle of scouring for individual parts. Additionally, a complete receiver offers better value for money than buying individual components(barrel ~$600, bcg ~$400 and receiver cover w/handguard ~$400 + other parts). 

Accessory Attachments

Buying an upper receiver that supports the attachment of accessories is always a better option, basically due to the fact that such capability allows you to customize the rifle according to your specific needs.

What Do I Need to Know Before Buying? 

These are the most common considerations shoppers should think about:


Although the receivers reviewed in this list are compatible with standard AR-15 lower receivers. It is only possible with the help of adapters and a different trigger assembly. It is important to note that MCX trigger installation is required to ensure proper operation of the upper receiver, whereas the adapter helps eliminate the use of a buffer tube on an AR after you install the upper. 

Legal Issues

Since the MCX is a compact platform. If your rifle falls under the definition of an SBR or pistol after switching the uppers, you’ll have to abide by certain legal restrictions such as obtaining a federal tax stamp, or adding only a brace to the pistol. These laws vary from state to state, so please check with your local laws before buying. 

Design Differences

While the MCX looks exactly like an AR-15, it features a different design. The MCX is a gas-piston operated rifle with a state of the art adjustable gas system. Additionally, the charging handle sits a bit high compared to an AR. Plus the MCX has a folding stock to help it cram into a backpack or something compact. 

Review of the Best Sig MCX Uppers

Now that we’ve discussed all the aspects of a Sig MCX upper, it’s time to review the best options available on the market. Apparently Sig is the only manufacturer of the MCX components, the major difference among the uppers mentioned here are dimensions, attachments and intended use.

Best Overall:
MCX 5.56MM NATO AR Conversion Upper


  • Chambered in 5.56 NATO
  • Two stage match grade trigger with crisp break
  • Includes all adapters and installation hardware
  • AR conversion upper compatible with AR lowers
  • Can also be used to convert other caliber MCX into a 5.56 NATO


  • None we could find

What Recent Buyers Report

The recent customer reviews focus upon the high quality and precise fit of this upper receiver. The upper is chambered in 5.56MM NATO which is a popular intermittent cartridge. The package includes all the essential hardware which justifies its price to a good extent.

Why it Stands Out to Us

The conversion assembly allows you to convert your AR into an MCX, without the need for switching ammunition caliber. Additionally, the upper comes with a crisp two stage match trigger which greatly enhances accuracy. The upper features an impeccable finish and complements the aesthetics of a standard AR lower receiver. 

Who Will Use This Most

The upper is ideal for range use, hunting and tactical applications. It is ideal for people who like to experience an MCX without changing the regular 5.56 AR caliber. Additionally, the crisp match grade trigger makes the upper suitable for competitions. 

Bottom Line

The Sig MCX 5.56MM NATO upper should be the first choice of an AR owner who wants to get the taste without spending a ton of money. The upper comes complete with all the necessary hardware to completely eliminate compatibility issues. 

Best for the Money:
Sig Sauer MCX 300BLK Suppressed Complete Upper


  • Suppressor-ready upper receiver
  • Does not convert your rifle into an SBR
  • Features a 16 inch long barrel for optimal accuracy
  • Chambered in 300 blk caliber for good range and stopping power


  • Suppressor is welded and can’t be removed
  • High price and may attract legal implications

What Recent Buyers Report

The suppressed MCX upper features an exceptional quality and finish, while being extremely easy to install. The upper comes complete with all accessories for compatibility and the included suppressor adds to its value. Users appreciate the quick installation and the value for money this upper offers. 

Why it Stands Out to Us

It is the only MCX upper with a suppressor on our list. Inclusion of a suppressor greatly improves the value of your firearm since it is an important accessory for tactical purposes. This upper comes chambered in 300 blk and requires minimal modifications to the rifle for installation. 

Who Will Use This Most

This upper kit is suitable for people who want to have a suppressor on their MCX build and don’t want to scour the market or put effort in hiring a gunsmith for installation. The suppressor has been welded to the barrel so it stays secure in all conditions and acts as a permanent muzzle device to counter legal clauses in some states. 

Bottom Line

The MCX 300blk suppressed upper is a very tactical replacement for your compatible lower receiver. The 16 inch barrel helps with accuracy whereas the suppressor helps with noise reduction for indoor range and tactical applications. The price may concern buyers on a budget. But overall it is a good product.

Best Sig MCX Rattler Upper:
Sig Sauer Upper MCX


  • 5.5 inch short barrel
  • Converts your AR into a MCX pistol 
  • Comes complete with adapters and mounting hardware
  • Great for compact storage and CQB or similar applications


  • Limitations with mounting stock in some states
  • Requires you to have a tax stamp and valid permission

What Recent Buyers Report

The upper fits perfectly on compatible lower receivers and features a perfect finish. While the price is high, it is still a very hard to find piece so buyers don’t actually consider this a deterrent. The upper is a high quality product with almost no negative reviews from users. 

Why it Stands Out to Us

This is a pistol upper receiver that is compatible with standard AR lower receivers. Plus it comes packaged with all the necessary hardware for installation. The barrel despite being short delivers amazing accuracy and the included trigger is of the highest quality. 

Who Will Use This Most

The upper will create a MCX pistol that will best suited for training and tactical applications. The short rifle will be ideal for CQB and can be used in a home defense situation. Additionally, the crisp two-stage match grade trigger included with the upper is quite suitable for shooting competitions. 

Bottom Line

While most people favor regular length carbines, this upper is for people who want to have a MCX pistol without paying the full price for it. The upper has been meticulously designed and delivers exceptional accuracy over short range. The upper comes complete and with all required hardware for easy installation and removal. 

4. MCX 300 AAC Blackout AR Conversion Upper


  • Available in 16 inch and 9 inch variants
  • Allows you to convert your AR-15 in an MCX
  • Chambered in the powerful and balanced 300blk caliber
  • Full length rail and M-Lok handguard for adding accessories
  • Pro 5


  • The trigger is not very crisp

What Recent Buyers Report

The Sig MCX conversion upper features an impeccable quality and finish. The package comes complete with respective adapters and trigger for easy installation. However, some users did mention the price factor and minor compatibility issues with the AR style lowers. Although, overall the buyers seemed satisfied with the upper. 

Why it Stands Out to Us

This upper works as a conversion kit to suit your AR style lower receivers. Plus it includes all the required adapters and the trigger for installation. This helps you save money which would rather be spent buying a brand new rifle. This upper is a complete and ready-to-shoot package.

Who Will Use This Most

The upper is perfect for people who like to customize their existing AR platform to draw the experience of shooting an MCX. The long 16 inch barrel helps with short to medium range shooting. Plus the accessory compatible design allows the user to get all the tactical features up and running within moments. 

Bottom Line

The Sig MCX AR conversion upper is a complete and ready-to-shoot package that allows you to shoot an MCX from your AR lower platform using 300 blk ammunition . The upper is easy to install and includes all the necessary adapters for the transition.


The Sig Sauer MCX is a tactical miracle developed according to the specifications of Special Forces. While buying one can be expensive, you can buy an MCX upper receiver to couple it with your standard AR-15 lower receiver. However, you must take care of the durability, compatibility, finish, performance and your desired application before choosing a suitable upper receiver. 

People Also Ask

The Sig MCX is a sassy, effective and desirable weapon which offers unmatched tactical and handling capabilities to the user. With the latest upgrades, an MCX upper can be coupled with a standard AR lower. Making it a very viable concept for AR-15 owners. However, there are still a few common questions lingering around in the mind of every prospective buyer. 

Is the SIG MCX an AR 15?

Looks, yes. Technically, not much. The Sig Sauer MCX is more compact, lightweight and has a different gas system than an AR. It uses a gas piston whereas an AR-15 uses a direct impingement system to cycle. While chambered in the same caliber, the MCX is great for CQB, whereas an AR can be used for long distance engagement. 

AR-15 and Sig Sauer MCX explained (Source)

Is the M13 a Sig MCX?

The M13 is a rifle featured in the famous FPS video game Call of Duty: Modern Warfare(2019). The M13 has been modelled after the Sig Sauer MCX rifle. It is very popular among COD players as a close to medium range weapon, due to its high rate of fire and low recoil. In real life, the M13 refers to the metallic disintegrating link designed for 7.62x51 belt fed firearms of the U.S Military.

Is the Sig Sauer MCX an Assault Rifle?

Yes, it is an assault rifle. According to the definition, an assault rifle is a rifle that fires an intermediate cartridge, can switch between firing modes (full auto, semi-auto and/or three round bursts) and uses a detachable magazine. Assault rifles are currently the standard rifle of all modern armies in the world. 

How Much Does a Sig MCX Cost?

These rifles can cost anywhere between US $1,800 to US $2,500. It depends upon the variant of the series. For example, a Sig MCX Virtus 5.56 with a 16 inch barrel costs $1,899 and a Sig MCX pistol with an 11 inch barrel costs $2,000. Whereas a Sig MCX Rattler 300 blk costs $2,299.

Michael Lutes is the managing editor and owner at Gun Mann. He is a veteran, gun enthusiast, 3 gun competitor, and 2a advocate. Mike has a passion for innovation and education across the industry to create great content, training, and insights from the best and brightest.