Best AR-15 Piston Uppers & Conversion Kits: 2017

It seems like everyone and their mom makes a piston-driven AR-15 these days.  And with good reason.

Piston-driven guns run cleaner and cooler than a standard direct impingement (DI) system, making them a big draw for high volume shooters such as those who shoot competitively like in 3-Gun.

They also just make all around great guns if you want to get into AR-15’s a bit more and try something different.

Who knows?  You might just fall in love.

PWS MK1 Mod 2 Complete
PWS MK1 Mod 2 Complete

Unfortunately, not everyone has the kind of cash required to pick up a whole new gun just to give this fancy shmancy piston thing a try…which is totally understandable.

So what do we do?

Adams Arms (AA) Piston Conversion Kit
Adams Arms (AA) Piston Conversion Kit

One option is to simply switch out the upper receiver with a piston-enabled upper receiver and be on your merry way.  Or you can use a conversion kit to change your DI system into a piston one.  We’ll cover our top picks in each!

If you can’t wait…here are our picks for best AR-15 piston uppers and conversion kits:

I’ve used all of them…but first let’s go over why you’d even want a piston AR in the first place.

Getting a Piston AR-15 Without Breaking the Bank

Well, if you’re anything like me when I started out, you probably already have a cheaper (but no less awesome) direct-impingement AR-15 laying around.  

Aero MC-15M
Aero MC-15M

If that’s the case, then you can just pop your current upper receiver off, and slap on a new piston-driven upper.  It’ll work just fine with your lower.

AR-15 Lower Receiver
AR-15 Lower Receiver

If you don’t already have an AR-15, I highly recommend picking up a DI gun first before springing for a much more expensive piston-driven one.  If you need help choosing your first AR, I also recommend giving our updated AR-15 Buyer’s Guide a look.

So, what piston-driven upper should you get?  How do you choose?

Well, I’ve tried out way, way, waaaay too many of these things (just ask my fiancé ) so I’ve got a list of what I think are the best piston uppers currently out there.  

Why Choose a Piston AR-15

This is going to be a bit of a Coke vs. Pepsi, Ford vs. Chevy, Superman vs. Goku type of deal, so it’s important to understand right away that a lot of this is going to come down to personal preference.

Superman vs Goku
Superman vs Goku

However, there are some tangible benefits to choosing a piston AR.  You’ll have to decide if they’re worth it.

Also, the correct choices are Coke, Ford, and Goku, and you can tell me why I’m wrong in the comments.

Benefit #1: No gas blowback into the breech

With a piston AR, you don’t get the gas and powder fouling into the breech like you do with a standard DI firearm.  Instead, you get just a small amount of powder fouling in a small, contained area around the piston itself.

Why does that matter?

Well, with a standard AR-15, you get exhaust gases and powder, and all that crud and gunk that comes from firing a gun dumped right back into the breech.

Direct Impingement
Direct Impingement

This means all that junk winds up in your lower, which makes for a much dirtier firearm, and much more frequent cleanings if you don’t want your gun to start having some issues.

So basically, a direct impingement gun shits where it eats, which is…not ideal.

Piston AR Animation, Adams Arms
Piston AR Animation, Adams Arms

Meanwhile, a piston AR funnels all that gas and powder fouling into a contained area (face of the piston), which makes a piston AR a much easier beast to clean and maintain.

Benefit #2: Heat Displacement

You know how other guns get hot when you shoot them?  Yeah, same thing happens with AR-15s.

However, for really high volume shooters, like say if you have a legal fully automatic lower, or you shoot competitively, you can keep your gun a little bit cooler by swapping to a piston system.

AR-15 Bacon Cookoff, RescueHumor1
AR-15 Bacon Cookoff, RescueHumor1

This is because, again, you’re not dumping hot, nasty gases into the main body of your firearm anymore and are instead keeping things contained.

Downsides to Piston AR-15

Now, it wouldn’t be much of choice if that was the whole story.  There are some downsides to the piston lifestyle that I want to go over as well.

First, they’re pricey.

As in, some of these upper receivers alone cost as much as fully-kitted direct impingement gun, pricey.  But, for some people that’s okay.

Khajit Has Wares If You Have Coin
Khajit Has Wares If You Have Coin

Second…parts can be a bear to find and match up properly.  Piston systems aren’t necessarily standardized like direct impingement systems.  So if you go with one manufacturer, you’re stuck with them.

So make sure you choose one that has a good track record and will be around in the future.

Lastly, since there’s more metal stuff in the front, the gun can become front heavy.  I haven’t found this to be a serious hindrance but it’s a little different from your normal DI gun.

So, with all that being said, let’s get into some of the best piston uppers and upper conversion kits on the market.

Best Budget Piston Upper: Rainier Arms Base Piston

Rainier Arms Base Piston AR
Rainier Arms Base Piston AR


  • Mil-Spec upper
  • Voodoo Barrel: 5.56mm NATO 14.5″ Government Contour
  • Barrel Material: Melonite Coated 4150 Chrome Moly Vanadium Steel, black
  • 1:7 Twist
  • Muzzle Thread Pattern: 1/2″-28
  • Barrel Finish: QPQ Melonite / Black Nitride
  • M4 Feed Ramps
  • Bolt Carrier: 1-Piece w/Integral Piston Strike Face
  • MP Tested Bolt

The Rainier Arms Base Piston AR ($575) puts these uppers together from parts kits, and I have to say they do an excellent job. This one is actually built from the Adams Arms Midlength Conversion Kit ($275) that is also on my best conversion kit list.

The mid-length size is the best of both worlds and splits the difference between the shorter carbine and longer rifle uppers, which makes this a bit of a Goldilocks upper…least for my purposes.

Midlength Shooting Target
Midlength Shooting Target

I think the midlength platform is probably the best place to start out for most newbies, and it’s a great starting point for those who just want to try something different as well.

You get a longer forearm than with a carbine length, which makes for an easier shooting experience, but you don’t have too much barrel slowing you down like you do with a rifle length gun.

This is especially an issue when you’re trying to move during a competitive match, a home-defense scenario, or in the confines of a deer stand.

Many a deer has been spooked by a hunter banging their barrel against something in the stand.  No that’s not a euphemism.

Spooked Deer
Spooked Deer

The only problem with it, assuming it has all the other features you want, is the handguard. It’s a little bit limiting (not to mention boring), so I recommend picking up a drop-in upgrade.

Overall, this was my first piston upper, so it has a special place in my heart.  And if you’re looking to dip your toe into this area, it definitely won’t disappoint.  Sometime’s it’s out of stock so check out Rainier too.

Best Value Piston Upper: Adams Arms Tactical EVO Upper

Adams Arms (AA) Tactical EVO Upper
Adams Arms (AA) Tactical EVO Upper


  • 5.56mm NATO 16″
  • Barrel Material:Chrome Moly Steel
  • 1:7 Twist
  • Muzzle: Pinned A2 Flash Hider
  • Barrel Finish: Melonite / Black Nitride
  • Bolt Carrier: Black Oxide Coated Steel
  • Free Floated Aluminum Forearm
  • M4 Feed Ramps

The Tactical EVO ($720) from Adams Arms is the industry standard for a solid, reliable, piston upper.

It comes with a very nice aluminum handguard that has a full flat-top rail that connects seamlessly with the rail on top of the upper giving you the ability to mount every kind of sight, scope, laser, can opener, and tactical assault coffee mug your heart desires.

Battle Mug
Battle Mug

Seriously, the rails on this thing (the gun, not the coffee cup) are incredibly functional, and (re)movable so you can place them where you want, or lose them completely for a more high-speed, low-drag look.

Beyond that, the upper functions flawlessly with proper maintenance when used in conjunction with a quality mil-spec lower. It is a bit more expensive than Rainier’s Base model, but it’s worth it if you have the cash, or want to upgrade a little bit.

Or if you need four lights and a laser to feel safe.  Hey, no judgement here.

Mall Ninja AR-15
Mall Ninja AR-15

Ok…a little judgement.

Best Overall Piston Upper: PWS MK1, MOD 2

PWS MK1 Mod 2
PWS MK1 Mod 2


  • Barrel Length – 14.5″ (Pinned to 16″)
  • Overall Length – 23.4″
  • Gas Piston System – Carbine
  • Barrel Twist – 1:8
  • Caliber- .223 Wylde
  • PicMod Rail System Handguard
  • Forged upper
  • Adjustable Gas Block

If you have the money and want the very best possible piston upper, get the PWS MK1, Mod 2 ($1299)

If you don’t have the money, and want the very best possible piston upper, get this one anyway.

If the fecal matter has hit the fan, the apocalypse has come, and you’re digging through Rainier’s warehouse to try and build something that will help you survive the wasteland that our world has become, get this one.

Rick Wishes He Had The MK1 Mod 2
Rick Wishes He Had The MK1 Mod 2

Seriously, all kidding aside, Primary Weapon Systems has made what is, in my mind, the very best drop-in, no-fuss, shoot-all-day, piston-driven upper on the market today.

This upper has all the features you could possibly want, including the unabashedly cool PicMod System that allows you to use Keymod and Picatinny attachments.

It also has a forged upper receiver, making it stronger and yet lighter than comparable billet receivers.

Finally, it has an easy-to-adjust, low-profile gas block that will allow you to dial down the felt recoil of the gun to get the best possible accuracy and performance possible. This is also key if you’re going to run a suppressor on your gun.

PWS MK1 Mod 2 Complete
PWS MK1 Mod 2 Complete

All in all, this is the one I recommend the most.  Its sitting on top of one of my competition rifles right now, and I have no plans on taking it off anytime soon.

Best AR Piston Conversion Kit: Adams Arms Adjustable Gas Piston Kit

Adams Arms (AA) Piston Conversion Kit
Adams Arms (AA) Piston Conversion Kit

Now, if you don’t want to buy a whole new upper, there are also a number of gas conversion kits out there that will take your DI gun and convert it to a piston system.

I’ve tried several.

I hated all of them but this one.

The Adams Arms Piston Conversion Kit ($275) will let you convert your DI upper into a piston upper with a minimum amount of fuss. I love it, and I’ve used two of them now and I couldn’t be happier. I can’t really recommend any other kits in this category because:

A) I haven’t found another one that I like, and…

B) There aren’t really any other ones that are worth your time.

This kit comes with the same adjustable gas block that comes in the Adams Arms upper I told you to buy just a minute ago, and it is all together the best kit to toss in a mid-length rifle.  They also have kits for rifle and carbine versions as well.

Final Thoughts

That about does it for this one guys and gals.

Those are my recommendations for choosing a piston based AR-15 upper.

I hope this was helpful, and I hope that if it wasn’t, you’ll tell me why in the comments below…


  1. Very interesting article. I already have a carbine so I’d like a longer length barrel for distance. Does the Adams Arms (or any other reputable manufacturer) make a piston upper with an 18″ or 20″ barrel?

  2. Great article. On the piston conversion kits, did you try the Superlative Arms conversion kit? If so, how does it stack up to your pick, the Adams Arms conversion kit?

  3. When converting from D.I. to piston, have you noticed any impact on tuning or does the piston system run pretty comparable? Also, being that there are moving parts more forward in the rifle, is this noticed during shooting? It seems like the barrel would “dip” when the piston resets. Great article, but it’s Coke, Ford, Superman, probably ‘cuz I’m old!

  4. I have a PWS MK216 in .308 with a long-stroke piston and it is an absolute dream to shoot. I would concur that the PWS is a top-notch AR platform in any caliber offered.

  5. I think piston is the way to go , patriot ordnance or adam arms?….mmmnnn……

    Another benefit to look at is avoiding all the exhaust blowback from the rifle. According to the diagram, the exhaust is going forward, instead in your face…..

    Anyhow, I think piston is the way to go , patriot ordnance or adam arms?….mmmnnn……

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