The AR-15 was designed as a combat rifle utilizing a direct impingement as the original technology, devised by Eugene Stoner in the early 60s.
Another ingenious solution developed by the brightest firearms designers of that time was the short-stroke gas piston system, applied by Mikhail Kalashnikov to the AK-47.
We will show you how these two things can work together to give you better performance. Check out some of the uses and benefits of gas piston upper receivers and then stick around for reviews of some of the best of these from the market today.
Comparison of the Best Gas Piston Upper Receivers
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How a Piston System Works
The need for AR piston-system rifles was not necessary - or to cite the words of late Col. Jeff Cooper - “An ingenious solution to a nonexistent problem.” Still, some manufacturers, striving for perfection released a line of piston-driven receivers that appear to be the ideal blend of AK reliability with AR ergonomics.
With the standard direct impingement system (DI), gas is deflected from the barrel through a tube and back into the upper receiver to perform the cycling. But it can build up a lot of fouling on the bolt carrier group. This residue can result in malfunctions.
On the other hand, a piston system utilizes a piston drive rod instead of a gas tube. The rod acts as an intermediary to exert force on the bolt carrier group to cycle the weapon. Instead of traveling through a tube, the propellant gas simply pushes the piston and then escapes out of the gas block well forward of the receiver.
Since there is almost no gas running back into the upper receiver, this system keeps the gun extremely clean and cooler than Stoner’s direct impingement system.
What Makes a Great Gas Piston Upgrade?
Knowing which characteristics and features make up a great gas pistol upgrade are key. You’ll need to distinguish those that are considered the best in quality and performance from those that are not. So you should be able to easily decide which one will work best for you. Here are some characteristics and features that should be at the forefront of your mind;
The price tag is always an important thing and the top concern for most budget shoppers. But a smart buyer knows that price is not the only deciding factor in purchasing a gas piston. You should find the best one you can afford in terms of quality and performance. Even if it means spending a little more on the higher end of your budget range, it’s still better than throwing money away on a cheap gas piston.
If you are not someone that has gunsmithing skills, you don’t have to worry because you’ll be able to install these gas pistons in minutes with the right kind of tools. Granted, there may be some pistons out there that require the professional services of a gunsmith. So if you lack adequate gunsmithing skills, you may want to find a model that is considered a drop-in.
Which Caliber(s) Is It Compatible With?
You’ll need to find a gas piston that will be compatible with your type of AR-15. If you fire 5.56 NATO rounds, you should find a piston upgrade that is compatible with that caliber. The same goes if you’re using .223 rounds, 300 AAC Blackout rounds, and so on.
Review of the Best Piston Upper Receivers
Below is a list of the three best AR-15 gas piston upgrades on the market. As you go through each one, look for one that matches your ideal description of an ideal gas piston upgrade. If you find one that matches your description, you know you’ve found a winner.
In this short list, you’ll find some of the best piston upper receivers presenting one of the biggest innovations in the development of the AR-15 uppers. Let’s take a look at the first gas piston upgrade on our list:
Best Piston Upper Receiver Overall:
Wolf AR-15 A1 Complete Upper Receiver 5.56 Piston
What Recent Buyers Report
New buyers were quite satisfied with this gas piston upgrade. They said that installation was a breeze and the upgrade helped the gas system operate without any malfunctions or reliability issues. One user even said it has helped upgrade his accuracy.
Why it Stands Out to Us
This gas piston upgrade is solid in construction and adds a lot of reliability to your rifle. On top of that, it does a good job preventing any kind of debris from entering your rifle and doing damage to the inside. So, if you want a gas piston upgrade that will do its best to keep the rifle clean without kicking up dust, this will probably be something worth investing in.
The Wolf A1 Complete AR-15 Upper Receiver is, in fact, based on the design of the R.O.C. T91. But it can be easily paired with any standard AR lower. Although it looks like any other M16/M4 clone, it offers the added reliability of the short-stroke piston system of the Taiwanese T91 military rifle. That model is internally similar to the Armalite AR-18.
Unlike most piston upper designs for AR-15, the A1 system is modularized and can be easily removed for cleaning and maintenance.
This upper comes complete with a protected front sight tower, a one-piece bolt-carrier group, and a charging handle. The package does not include a forward assist button rear sight. In addition, the 16.5-inch, cold hammer-forged barrel is topped with an A2-like flash hider. This flash hider has porting further back than normal to act as an effective compensator.
With an authentic charging handle and a handguard, the T91 piston upper fits any AR-15 or M16 lower receiver.
The only drawback we’ve heard about in this model has to do with the appearance of this handguard. However, this upper has a utilitarian foregrip that resembles the old American M16A1 clamshell. It provides a secure grip and protects your support hand with a heat shield, even with heavy fire.
This affordable and proven Wolf Arms piston upper is a good choice for home defense, recreation, or hunting. It’s also compatible with select-fire capable lowers, making it the perfect option for tactical applications.
Who Will Use This Most
This will be a useful gas piston upgrade you can install on most AR-15 builds, especially if you’re building one from the ground up. If you want the perfect gas system that is reliable right out of the gate, this gas piston upgrade should be a good addition to your build.
The Wolf AR-15 A1 Complete Upper Receiver 5.56 Piston might be right up your alley if you want a solidly constructed gas piston system that will give your rifle a boost in accuracy and reliability. Don’t be surprised if you see that happening immediately after installation.
Best Piston Conversion Kit Overall:
Adams Arms AR-15 P-Series Micro Block Gas Piston Conversion Kit
What Recent Buyers Report
As expected, the new buyers had nothing but good things to say about this gas piston upgrade. They said assembly wasn’t a challenge and the subsequent installation was easy and took as little as ten minutes. One user said the pistons were durable and did a really good job keeping the gas system functional.
Why it Stands Out to Us
This is a gas piston upgrade you can assemble rather easily. Once you do, you can hook it up to your carbine gas system. From there, you’ll be able to use some serious firepower to your advantage. If you want gas pistons that will keep your carbine gas system functional for a long time, this upgrade will certainly fit the bill.
Adams Arms produces their Tactical P-series of solid, reliable piston uppers designed for hunting, competition, or duty carry. The Micro Gas Block piston kit is a part of this series. It’s based on the short-stroke free-float piston design preferred by many AR owners.
This updated version weighs 40 percent less than their previous kit. The kit includes a compatible one-piece bolt carrier, installation rod, bolt spring, non-adjustable gas block, bushing with attached spring, and upper receiver bushing.
The advanced geometry of the Micro Gas Block expels carbon and gases forward, away from the operator. The installation instructions make converting the AR-15 from direct impingement to gas piston easy. However, the main issue is that it's not attached, as it would be with a factory piston.
Who Will Use This Most
Expect this to be a great gas piston upgrade system for users who want to keep their rifles clean and want reliable cycling without the jams and reliability issues that can cause headaches and frustration. If you’re serious about having a great gas system in place, these gas pistons will probably be something you can rely on.
The Adams Arms P Series is the perfect gas piston upgrade for those who have a carbine gas system. If your rifle has it, you’ll need a good set of gas pistons to help make it the best functioning part. This might be exactly what you need to achieve that.
Piston Conversion Kit Runner-up:
Superlative Arms AR-15 Adjustable Piston System .750" Clamp-On Gas Block
What Recent Buyers Report
Most recent buyers were quite happy with the gas piston upgrade. They were even more impressed when they realized they could easily adjust it to fit most gas systems. One user said it was easy to adjust so it could work well with his carbine gas system.
Why it Stands Out to Us
Another patented design comes from the Superlative Arms LLC. This one from SA offers an adjustable gas piston system for the AR-15 platform which is a relatively simple and effective DIY upgrade.
This kit is available in many configurations such as pistol, carbine, mid and full rifle-length. It’s also available as a clamp-on or with socket head cap screws. And of course, there are versions for both .750" or .625".
This gas piston upgrade is easy to adjust and therefore, easy to use. It eliminates all the guesswork of what kind of gas piston upgrade will fit you best because you have them all in one kit. You can make the right kind of adjustments, set them up for your gas system, and you’re done. Once installed, you’ll have even better reliability and smooth cycling, among a few other benefits.
The package included a piston block assembly, a carrier without the bolt, the gas block plug, bushing and insert tool, and the hex keys.
This system will function in rifles chambered in .223/5.56 x 45mm NATO. This model features SA’s proprietary “Bleed Off” gas piston system where the gas flow is regulated by bleeding the gas out of the block instead of restricting the flow like conventionally-adjustable blocks.
There are 30 locking gas positions with audible clicks to choose from for many types and brands of rounds. In other words, you may switch between bullet weights or move from suppressed to unsuppressed fire without any operational problems or causing the system to be under or over-gassed.
While this upgrade kit appears to handle any bullet weight just fine, there is a noticeable difference in recoil depending on suppressor use. It’s not extreme, but it is noticeable.
Who Will Use This Most
This gas piston upgrade will be your cup of coffee if you are having a hard time looking for a suitable gas piston upgrade that works. If you want something that is built to last and easy to adjust on-the-fly, this might be what you’ve been looking for all along.
The Superlative Arms AR-15 Adjustable Gas Piston Upgrade is a nice package of gas pistons that can be added on to any gas system. All you have to do is make some adjustments to ensure it will fit your gas system and you’ll be set for a long time.
4. Adams Arms AR-15/M16 Piston Tactical EVO Upper Receivers
The Adams Arms system allows your rifle to run cleaner, cooler, and more reliably due to its patented short-stroke gas piston. Their enhanced piston system involves a small chamber specifically designed to capture the gases.
The company developed its operating rod with a small cup on the end into which the regulator is inserted. It resembles the old “short stroke” piston solution found on the SKS and M1 Carbine.
This mid-length piston system incorporates a Samson Manufacturing Evolution extended free-floating 12″ forearm. This gives you a longer sight radius and a more extended, ergonomic grip.
The re-designed piston upper receiver is forged from 6061 T6 aluminum and features an A4 13-slot Picatinny-cut flattop rail and M4 feed ramps. They provide EVO uppers with their 16"-long standard barrel topped with an A2 flash hider and an adjustable gas block. The gas system can be regulated for use with sound suppressors. It also has a shut-off to allow single shot fire with no cycling, if needed.
For all its strong points, serious shooters may not be content with the lack of adjustable settings.
5. Adams Arms AR-15/M16 5.56 16" Basic Piston Upper Receiver
The Adams Arms economic Basic Piston Upper Receiver meets all the requirements of a short-stroke piston system. It helps eliminate hot gas and debris from the action upon firing. That creates a smoother feeding, less violent cycling, and reduced felt recoil.
This basic mid-upper is machined from 6061 T6 aluminum forging and features a 13-slot Picatinny-cut flattop rail and M4 feed ramp cuts.
The Adams Basic Piston Upper Receiver is based over 16" barrel with a mid-length gas system for smoother recoil impulse and a longer sight radius. Along with the 16" Melonite-finished barrel and A2 flash hider, this assembly includes a one-piece bolt carrier group made of solid steel, a piston tube, a steel piston, a charging handle, a Delta-ring assembly, and a Picatinny-rail gas block.
Additional features include an M4-style carbine handguard and a forged A3 flattop configuration with a 13-slot Picatinny rail. The low-profile railed gas block is adjustable for regular fire or for firing with a suppressor. The gas-off features enables single-round firing without cycling.
While the gas piston operating system keeps the gun cooler, the hot gases are directed at the railed gas block. So it’s a good idea only to use a metal front sight so it won’t melt atop an overheated gas block.
6. Syrac Ordnance AR-15 Adjustable Gas Piston System
Just to start on an interesting note: Jason Adams, the founder of Adams Arms, also founded Syrac Ordnance. Syrac's adjustable gas piston system was developed in collaboration with Superlative Arms. So all the products we’re looking at here are closely related.
Generally, all piston systems work the same. But the Syrac's Gen II series of low-profile, fully-adjustable systems offers one of the lightest piston kits on the market. It can also fit under most handguards.
Syrac offers one of the most sophisticated adjustable gas blocks capable of transforming a punchy 5.56 AR-15 to a flat and soft-shooting firearm. It’s amazing the difference it can make in the same gun, just by reducing gas pressure. This new piston system features a gas adjustment screw that is accessed from the front of the gas block.
The gas block has 24 gas adjustment settings, allowing you to fine-tune your rifle to the type of ammo you use. In addition, the adjustable gas block can completely turn the gas off, which would cause the rifle to not cycle at all.
In order to lock in the adjustment, Syrac Ordnance has developed a locking detent for the screw. That way, the adjustment will never shift accidentally, even under recoil.
There are a couple small complaints about poor instruction and customer service. Also, quality control seems erratic with these.
The Alternative: Upgrading With a Kit
In addition to the more common complete AR-15 piston upper receiver, another recent trend is the piston conversion kit.
We all agree that piston operating systems keep the bolt carrier cooler and cleaner, but they also include more moving parts. While it requires no specialized tools or gunsmithing for mounting, this hardware isn't easy for people unfamiliar with the AR's installation process.
Why Choose a Piston System Over Direct Impingement?
The AR-15 is an extremely customizable platform. But, as with nearly everything with this rifle, the upgrades you make depend a lot on personal preference. And of course, your intended use comes into play, whether it’s competition, hunting, or home defense.
Shooters who prefer piston-driven rifles usually state that these arms are cleaner, cooler, and more reliable than the direct impingement system traditionally used in the AR-15/M16 platform. They consider them a good solution for high-volume fire in training classes or for those who shoot competitively in three-guns.
We also tend to agree with the line of thought that gas-piston operating systems work best on a carbine or PDW guns with barrels ranging in lengths from 4.5″ to 12″. This is due to the generally-accepted rule that the longer the gas system (tube), the better the direct impingement gas system will perform.
On the flip side, gas piston technology generates more felt recoil. It also tends to be heavier than impingement rifles. In addition, piston-driven guns are less accurate, especially for follow-up shots. Finally, since these systems are less common than DI ones, they tend to be more expensive.
Replacing the Upper Receiver with a Piston-Compatible One
While the piston system alters the mechanics and timing of an AR, the geometry of both concepts is the same. The unmatched modularity of the AR allows you to utilize both systems on the same lower receiver by swapping upper receivers out. Because the DI and piston systems operate independently of the lower receiver, you can switch between them on the same lower.
As the AR is the most adaptable and versatile rifle of our time, you can simply alternate the standard upper receiver with a piston-enabled version. By simply changing the complete upper receiver, the shooter can have an AR-15 upper receiver group with its own receiver, barrel, sights, muzzle device, gas system, and bolt carrier group. Alternativelt, you can choose to use a conversion kit to change your direct gas impingement system into a piston one.
Of course, you should note that some of piston upper receivers alone cost as much as a complete direct impingement gun. Besides the cost, another disadvantage is the non-compatibility of the gas piston-equipped AR-15's with .22LR conversion kits.
Piston replacement parts are expensive and hard to obtain. In addition, piston systems are not necessarily standardized like direct impingement systems, so they are not interchangeable between manufacturers.
Over the years, more people have become aware of how altering the gas system on an AR-15 can affect overall satisfaction with the gun. Piston conversion kits or dedicated piston upper receivers offer cleaner use of the rifle.
This substitute for the direct impingement system has gained traction in many quarters. Like all changes, it has its pros and cons. But making the change is relatively simple and you can give it a try as part of enjoying all your rifle has to offer!