The AR-15 platform has indeed gotten a bit stale. Everyone and their illegitimate cousin twice removed makes a version of the gun these days, and for most manufacturers all they actually do is grab a barrel from one supplier, a receiver from another, slap their branding on it and call the thing “new.” And for most consumers, that’s good enough. But Adams Arms has gone a few steps further. Not only have they completely re-designed the gas system to use a piston instead of direct impingement, but they go to the trouble of making their own parts — barrels included. While that’s all very impressive, as always the proof is in how well the gun actually runs. And even on that end, the company does things, well, differently . . .
Having reviewed few guns in my time, I’m used to companies putting conditions on my ability to test their guns. “You can have it, but it needs to be back in three weeks.” “Use only brass ammo, and don’t feed it after midnight.” “Use only the provided lube.” So I wasn’t surprised when I reached out to the guys at Adams Arms about testing out one of their piston-powered AR-15 rifles and they added a caveat of their own. But it wasn’t something I was expecting. Here’s the direct quote from their email:
Would you be willing to beat the crap out of our stuff and do your best to break it under real world application? If so were in.
I had never heard a firearms manufacturer say those words before and it was music to my ears. I was going to be given free reign to try and kill their gun, and given the design that appeared to be a pretty tall order. So I asked them to send me a SBR-length upper receiver as well, since the higher pressures involved with that gas system length would do a lot of the stress testing for me.
One day a few weeks later, the whole package arrived on my doorstep. So naturally, the very first thing I did was take it all apart and find out how it works.
The AR-15 was designed to use a “gas expansion” system, where a gas tube feeds directly into a piston in the bolt carrier group. It’s an effective design that works great most of the time. But when the gun gets dirty, it has a tendency to malfunction. Not that it takes long to get filthy — since the gas port empties directly into the chamber, the bolt carrier group can go from a shiny nickel boron coating to a grungy, gritty black in only a few minutes.
Adams Arms, however, has designed their piston system to avoid that issue. They keep the gas contained within a small chamber, instead using a piston to transfer the energy needed to cycle the action to the bolt carrier group.
The impact of that design is obvious: the upper I’ve been shooting hasn’t been cleaned once, and even after thousands of rounds downrange the bolt is still clean. You might notice that there’s one unclean part: the chamber specifically designed to capture the gasses. The way the piston system works is that the operating rod has a small cup on the end into which the regulator is inserted. The system uses that cup not only to align the operating rod so it slides into the upper receiver properly, but also to contain the exhaust gasses that are bled off. The result is an immaculate gun.
The concept is well established — trying to mate the reliability of the AK-47 with the accuracy of an AR-15. But in this case, it seems like their design got a little drunk one night and had a one night stand with an SKS instead.
The Adams Arms system is a “short stroke” piston similar to that used in the SKS and M1 Carbine, meaning that the bolt carrier is only being acted upon for a very small period of time before physics and momentum carry the reciprocating mass the rest of the way through the reloading cycle. It’s the more common format for a piston-based AR-15, but companies like PWS believe that a “long stroke” system (like that used in the AK-47) is better. Either way, the Adams Arms system suffers from the same drawback as all of the other systems, namely that it allows the chamber to open much earlier than with gas expansion (direct impingement) systems. The reason is that pistons force the bolt open immediately, but gas expansion needs time to pressurize the piston before it starts unlocking the bolt. The result is more exhaust coming from the ejection port, which you can see in the video.
So, the gas system works. And I have to admit, it’s great. I’ve done everything I could think of to get it to choke, including running without any lube, burying it in the Texas dirt for a bit, and running the piston without the spring attached (hey, what if you lose it?). In each case the gun continued to function without any issues. So long as the regulator was set to the “normal” setting and not “suppressed,” that is.
The regulator is probably my only complaint about the Adams gas system. For serious shooters, the ability to “tune” your gas system to where you want it is getting close to mandatory. “Normal” and “suppressed” settings are nice, but having a little more granularity wouldn’t be a bad thing. Thankfully Adams Arms has fixed this with their latest gas system regulator design, which has a bunch of different settings so you can tinker to your heart’s desire.
Out on the range, the ergonomics of the gun were right where you’d expect for a “run-and-gun” setup like this. The rifle is very light, and the handguards extend past the gas block allowing you to get a better grip on it. Due to the operating mechanism the gas block needs to be bigger than normal, but Adams decided to incorporate the top of the gas block into the picatinny rail instead of trying to make it disappear. It’ll get hot when you’re shooting so Magpul BUIS are right out, but a metal sight would work just fine.
As is usually the case, the Evo’s trigger is the standard “meh” trigger you’ll get on most factory AR-15 rifles. It’s a bit squishy and not really conducive to shooting tight groups. Again, that’s par for the course for run-and-gun rifles. For most higher level shooters, the very first thing they’ll want to do is slap their trigger of choice in there. So while it’s not really a major concern for those with more experience, we test guns in their “stock” configuration and the trigger is part of that.
The rifle (initially the 14.5″ with a pinned and welded flash hider) works as advertised, but there was one variable left to test: accuracy. And that proved to be a bit of a sticking point.
This isn’t good. I shot this at the standard 100-yard distance using a bipod, sandbags, and the same scope I had just used to test a Ruger SR-762, so I was pretty sure that I wasn’t the cause of the inaccuracy. And while the horizontal variation in the bullet impacts isn’t very much, that’s about a 3-inch spread vertically. It looked to me like there was a problem with the gas system causing the shots to wander. Naturally my first call was to the guys at Adams Arms, letting them know about the problem, and once I shipped back the 14.5″ gun they shipped me out a new 16″ rifle
As this was a new gun, I had to start from scratch. Some malfunction testing, a little light torture and a few hundred rounds later I was satisfied that the rifle performed as well as the previous one in the basic battery of tests. The only question left to answer was whether the rifle performed better than its predecessor.
Using some 77gr “match” grade rounds (Federal Premium in this case) I was able to get this roughly 2 MoA group out of the gun at 100 yards using the exact same scope and setup as before. Just to test the barrel, I tried the upper on my competition lower receiver (with a Geissele trigger) and I was able to get right around a 1-inch group. But since that was with a different lower, it doesn’t really count.
So the Evo’s accuracy was par for the course for a “gunfighter” rifle, but it’s good to know that you can significantly improve it just by swapping out the trigger.
The Adams Arms rifle is good, but it has a lot of potential being wasted in the current configuration. A more adjustable gas block, a better trigger and probably a better stock, too would put this gun into the running to be one of the better guns I’ve tested recently. And – what do you know? – they released a gun at the SHOT Show that fixes exactly those issues. So if you want a good gun to “run and gun” and possibly upgrade later, this is a pretty good investment. But with the 3-Gun version right around the corner I’d wait for that instead.
Ratings (Out of Five Stars):
All ratings are relative compared to the other weapons in the gun’s category. Overall rating is not mathematically derived from the previous component ratings and encompasses all aspects of the firearm including those not discussed.
Accuracy: * * * *
The gun is capable of much better accuracy if you swap out the trigger, but as-is, it’s not bad.
Ergonomics: * * * *
The gun fits me very well and everything on it works great. If I could nit-pick I’d put a bigger latch on the charging handle, and the exposed gas block can give you a rude surprise if you’re being too aggressive in your grip.
Ergonomics Firing: * * *
It might just be me, but it feels snappier than a normal AR-15. And that trigger is only meh.
Ease of Maintenance: * * * * *
The gas system keeps the gun clean, and among the piston systems I’ve seen this one is among the easiest to disassemble and re-assemble. Works like a charm.
Reliability: * * * *
The gun runs 100% perfectly every time. I’m removing one star due to the accuracy issues on the first gun, since there might be some additional variation in the quality that I’m not seeing. But if your gun doesn’t work right, the guys at Adams Arms seem to be more than happy to work with you to make it right.
Customization: * * * *
The only difference between this gun and the standard AR-15 is the gas system. Everything else is interchangeable, except the bolt carrier group.
Overall Rating: * * * *
It’s a great start, but the gun is capable of much better things than the current configuration allows. Based on features alone the gun would be about a 3.5, but since the rifle’s MSRP is well below the asking price of other common piston-powered AR-15s such as the Ruger SR-556 (and the street price is even better) it gets knocked up a half star. But slap a better trigger in there and maybe a better charging handle and we’ll see about giving it a better rating.