Building a rifle on the AR platform can be exciting, tedious, and even nerve-wracking at times. Not only do you have the complete autonomy to create the perfect gun for your shooting style and use case, but you can do it piece by piece at your own pace, and according to your budget. When building your AR-15, one of the biggest decisions you’ll need to make during your build is which upper to use.
Most shooters start with a cheaper AR-15 upper so that they have something they can shoot while they get their ideal parts list assembled. This often means that whether you buy a pre-assembled gun or build yours from scratch, you’ll have a direct impingement upper since they are far cheaper than a piston upper. Though this doesn’t mean that once you have the funds you can’t buy a piston upper to further customize and improve your AR-15.
The AR platform is one of the most popular shooting platforms around, and it only gets more popular by the day. One of the biggest and best benefits of popularity is the abundance of quality shooting parts and accessories. This even applies to major mechanical components of the AR-15, like uppers, and means that no matter what you’re looking for you can probably find one to suit your needs.
That’s where one of the bigger problems come into the story, how do you choose from the countless piston upper options and piston conversion kits that are on the market? If you are new to shooting entirely, or just new to the recent options in AR-15 piston uppers, this flood of options can be intimidating and confusing. That’s why we’ve lined up the best AR-15 piston uppers and piston conversion kits that you can get for your new AR build.
Best AR15 Piston Uppers and Conversion Kits
- PWS MK116 MOD 2-M Piston Upper
- Barrett REC7 Gen II Piston Upper
- Stag Arms 8HSC Piston Upper
- Wolf Performance A1 AR-15 Upper
- Faxon Firearms ARAK 21
- Adams Arms Piston Kit
PWS MK116 MOD 2-M Piston Upper
The Primary Weapon Systems PWS MK116 MOD 2-M piston upper is one of the best drop-in piston uppers made today. The PicMod system lets you use just about any attachment under the sun, and the forged receiver shaves weight while adding strength. The low profile block gives you full adjustability over the felt recoil, so you can dial in your specific performance and accuracy needs.
- PicMod system facilitates Picatinny and Keymod attachments
- 1:8 twist
- 14.5” barrel pinned to 16”
- Forged upper
- Adjustable gas block
Barrett REC7 Gen II Piston Upper
While it is one of the most expensive piston uppers on the market today, Barrett is also a name that delivers performance, and their components demand top-dollar in most situations. It does have a carbine gas system, however, so those looking for a mid-length gas system should look elsewhere.
- 1:7 twist
- 16” barrel
- Enhanced KeyMod rail
- Adjustable gas block
Stag Arms 8HSC Piston Upper
For a budget AR-15 piston upper, you really can’t go wrong with the Stag Arms Model 8HSC. The Stag Arms Model 8HSC piston upper can be configured and ordered to comply with your state’s specific laws. It also has a single-piece bolt carrier with an integral piston strike face.
- 1:9 twist
- 16” 4140 steel, manganese phosphate coated barrel
- Samson Star-C free-floating quad rails
Wolf Performance A1 AR-15 Upper
The Wolf Performance A1 is an AR-15 piston upper that is based on the T91 Taiwanese rifle and lets the average shooter kit their AR similarly. This upper is ready to drop into nearly any mil-spec lower and delivers stellar accuracy. This upper can go from competition shooting to defensive situations, and even varminting without skipping a beat. The chrome lining lessens the impact of shooting steel casings.
- 1:9 twist
- T91 style handguard and charging handle
- Hammer-forged barrel
Faxon Firearms ARAK 21
Another high-end piston upper, the ARAK 21 looks amazing and performs so well that even the armed forces are taking note. The ARAK 21 uses the same piston system found in the AK-47 and a reversible charging handle that can fold forward to lower the profile. The dual ejector opening adapts lefties super-easy, and it even has an ambidextrous selector.
- Tons of barrel options including 5.56 NATO, 6.5 Grendel, .300 BLK, and 6.8 SPC
- Left-handed friendly
- The barrel can be changed quickly in the field
Adams Arms Piston Kit
One of the most reliable names when it comes to piston conversions is Adams Arms, and their kits will let you convert and direct impingement upper into a piston upper with a relatively little amount of effort. They come with an adjustable gas block, and with the recent upgrades to their P-Series kits, they’ve reduced the kit weight considerably.
- Available for mid-length and carbine rifles
- Lightweight makes it great for rifles that are prone to being front-heavy
If you currently operate a direct impingement upper diverts a portion of the explosively expanding gasses, as well as some of the remaining powder, and of course carbon-based fouling, backward to the receiver and breech. These gasses are forced against the bolt, pushing it back and cycling the rifle. There is absolutely nothing wrong with this method, and it has been in service for many years.
What a piston upper does in general, is to make the resulting periodic maintenance much easier and quicker for the end-user. Rather than sending the hot gasses back to the breech and bolt, they are used to push a piston instead. The head of that piston takes the lion’s share of the fouling, and vents the gasses forward and away, resulting in a rearward force that moves the piston.
At that point, the piston actuates a bolt rod, which moves the bolt itself. This is where the normal firing cycle continues as it usually would. The result is that the bolt stays much cleaner than with a direct impingement upper since there is a degree or two of separation, as well as a significant distance between the bolt and the vent.
Additionally, redirecting the gas in a direct impingement upper back to the bolt results in a significant heat build-up and retention in the gun. With a piston upper, the gasses are vented much farther forward, which means your gun will stay cooler, longer. This also means that where you’d normally need to stop shooting and allow a DI-upper AR to cool, you can shoot more with the piston upper before needing a cooldown.
One of the most noticeable drawbacks to a piston upper receiver is that they are much more expensive than direct impingement uppers. Not just by a few bucks either, we’re talking about a good piston upper sometimes costing as much as an entire direct impingement rifle with accessories. For a lot of people, a price tag is just a number, for other shooters, however, that number can price them right out of the upgrade.
Another caveat for anyone upgrading from direct impingement to piston operation is that they are far less standardized. This means that finding parts to match up when needed can be a huge challenge, and once you choose a piston upper manufacturer or brand, you’re often locked into buying from them when you need parts. This makes your manufacturer research crucial to your build and what you expect out of it down the road.
A big factor that some people find is a drawback and some find a beneficial feature is that upgrading or converting to a piston upper brings weight with it. Not an insignificant amount of weight either, and this can often make the rifle too front-heavy or unbalanced for some people’s shooting style or taste. If you’re expecting it, you can generally cope with it, but it will definitely be different than your previous direct impingement setup.
This is where you need to decide what you want from your gun, as well as what you’re willing to put into it. Since the big initial hurdle is likely going to be the price of your piston upper or piston conversion kit, you will want to think about how much you actively shoot now, because the piston upper isn’t going to give you any reliability benefits over a direct impingement gun.
If you want a gun that will permanently cut down on your maintenance needs in the future, price is no object, and you are looking to bug out to the middle of nowhere and never return, the piston upper is where it’s at. There are also the parts availability concerns, so using the example of a SHTF-gun, while you’ve cut your cleaning down you’ve also made the interchangeability of parts much less likely. If you stick with a direct impingement upper, you can swap out a generic gas block at just about any time, with one that you can find in nearly any other direct impingement gun.
To make the final determination, you’ll need to decide what’s important to you. There are several benefits and drawbacks to the upgrade, as well as a similar list of pros and cons for sticking with a cheaper DI setup.