Review: Adams Arms Mid Base Piston AR-15

We see a lot of ARs, a lot. Most are decently accurate, reliable, and durable. Standard direct impingement guns with one upgrade or another are common. It is a simpler system that’s easier to get right. Expensive, $1,000+ rifles are also popular. So, it is exciting and refreshing to see something different come to the table. The Adams Arms Mid Base features a short-stroke piston system with a convenient and user-friendly gas adjustment. It is the midlength version of the company’s popular P1 carbine. Both are practically identical in other features.

Piston ARs are nothing new, but they can be pricey. The Adams Arms design works well and comes in at a price point that provides an excellent alternative to the standard budget D.I. AR-15. If you want to run your AR rifle hard and fast, but hate cleaning the bolt, you need a short stroke piston-operated rifle.

Adams Arms on brick
The Adams Arms Mid Base is ready for use.

Adams Arms Features

The Adams Arms Mid Base rifle features a 16-inch barrel, with a 1:7 twist rate and is chambered for the 5.56 NATO. The short stroke gas piston system rides under a midlength M4-style handguard. As it comes, it’s very thick in order to house the gas system, but it works well. Additionally, the rifle incorporates a standard 6-position collapsible stock, as well as an A2 pistol grip and flash hider. Let’s be honest, you’ll want to upgrade and customize those for yourself anyway. This keeps the initial cost down. 

The flat-top receiver features the standard Picatinny rail for optics, but there is a small section on top of the gas block as well for mounting your front sight. Overall, the rifle feels solid. There is no slop or rattle between the receivers, no grit when you’re working the action, and the safety clicks nicely into place. The standard G.I. trigger pulls at around 6–7 pounds. This is one area that could use an upgrade, especially if you want to stretch out to further distances

Because of the piston gas system, there’s no gas key on the bolt carrier. Instead, it is one solid piece and full-auto rated. This is a more durable design, as this is a point that can shear off under repeated hard use. 


  • Caliber: 5.56x45mm NATO (accepts .223 Rem.)
  • Barrel: 16-inch, 4150 steel M4 contour with 1:7 twist
  • Finish: QPQ Melonite/Black Nitride
  • Overall Length: 32.5 inches (collapsed)
  • Weight: 6.2 pounds
  • A2 flash hider, 1/2″-28 thread
  • M4 feed ramps
  • Short stroke, piston-operated, midlength gas system
  • Picatinny railed 0.750-inch gas block with 3 adjustment settings
  • Full-auto rated bolt carrier with integral piston strike face
  • Flat top, optics-ready upper receiver 
Adams Arms gas system
Here you can see the gas system separated out.

Adjustable Gas System

The hallmark of the Adams Arms rifle is the adjustable gas system. Under the front sight post, the gas block features an adjustment knob. Simply depress the spring-loaded button and turn the knob. When facing the muzzle end of the rifle, turning the knob clockwise once will cut the gas to 50%. Two turns will eliminate the gas and essentially make the gun single shot. Turning the knob counterclockwise will unlock the gas system for removal.

Once unlocked, it simply slides out for easy cleaning and maintenance. When the knob locks into position, you will hear the spring-loaded button click back into place. The standard 100% gas setting has the button facing up at 12 o’clock. 

The version reviewed has three gas settings: 100%, 50%, and 0% for standard, suppressed, and single-shot fire respectively. Adams Arms also offers an upgraded version for those who really want to dial in the gas system to their specific rifle and ammunition load. It incorporates 5 percentage options (100, 74, 53, 32, 11) and an optional low-profile gas block option. This is nice, but not necessary. I’m assuming this is mainly to allow the use of standard free-float handguards of the shooter’s choice. Currently, you are limited to what will work around the larger gas system setup. 

Pink torso target
The Adams Arms Mid Base averaged 1-inch groups at 25 yards.

Range Testing

So, how did this gas system fair at the range? Simply put, it ran great. I had no malfunctions in the 100 rounds I fired. This is a limited sample, and we’ll see how it does in further testing. However, it hasn’t hiccuped so far. I even tested the single-shot, no-gas mode. To no surprise, it functioned as intended. You must manually cycle the rifle after each round fired.

I did not have a suppressor on hand, but I hope to test out the 50% gas function in the future and will provide an update. I fired a mix of PMC and Armscor 62-grain brass target ammo in Magpul PMAGs. This is optimal bullet weight for the 1:7 twist barrel. 

It tested the Mid Base rifle with a UTG Accu-Sync red dot optic. This is a great lightweight optic with no magnification and a 3 MOA dot. After an easy sight-in, things were up and running. I fired both rested and standing to ensure nothing interfered with the gas system and reliable cycling.

Adams Arms gas block
Here you can see the adjustable gas block and push button.

My supported groups averaged around 1-inch at 25 yards. I’m still working on my rifle shooting, but this is better than my groups in the past. I’m sure the Adams Arms can make even a novice shooter look decent. We’ll see how it continues to shoot, stretching farther out in future testing. 

Final Thoughts

In a world of competitively-priced direct impingement ARs, it’s nice to see another solid piston offering come to the table, especially for the price. For well under $1,000, you’re getting one helluva rifle that is done well, with great gas adjustment features. That leaves you a lot of room to upgrade and tailor the rifle to your needs. I’m excited to keep working with the Adams Arms Mid Base and look at some upgrades to take it to the next level. 

Do you prefer a D.I. or piston AR-15? What do you think of the Adams Arms Mid Base? Share your thoughts in the Comment section.

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