Review: AR57 The Budget P90

57Center makes the AR57. It is an upper receiver for your AR lower to shoot 5.7x28mm ammo. The only other guns that shoot this ammo is the FNH P90 and their handgun the Five Seven pistol. I got this pistol/SBR upper with a 6″ barrel. 57Center offers their uppers with a 16″ and 12″ barrels. The upper receiver itself stays the same regardless of barrel length.

The AR57 uses a P90 magazine. For those not familiar with the P90 and it’s magazine, the magazine holds 50 rounds of 5.7x28mm but they are arranged perpendicularly to the body of the magazine and gun. Spring pressure pushes the rounds out like a traditional magazine. However the feedlips have a ramp, think of a multi level car garage. So the cartridges sort of drift 90 degrees down the ramps to line up with the bore and chamber.



The AR57 upper has a cutout to allow for this magazine to lay on top of the upper receiver.

13173978_10154239360265337_6723076848741908236_n IMG_3264

The position of the magazine is necessary for the function of the gun. However it does present issues with mounting optics. The AR57 upper has two sections of top rail. A short one at the front of the handguard and a medium length rail at the back of the receiver. You can mount iron sights like I have with MBUS. However that limits your optic options. As you can see above, there is only room for a red dot. You could mount a scope on this setup but it will take up most of the top rail. Putting a scope on this setup does have its own issues, such as the scope will be in the path of the magazine so you would have to insert the magazine sideways and then down.

I opted for the 6″ barrel upper since I wanted to tuck my SilencerCo SpectreII back and under the handguard.



The handguard is rather narrow so while you could possibly install a flash hider I do not think it would be a good idea. Remember the AR pistol with the muzzle brake under the handguard? Only a suppressor or even a faux suppressor would be safe to use with this upper receiver. Obviously that is not an issue for the 12″ which the muzzle protrudes just past the end of the handguard. And the 16″ barreled version has a rather long barrel past the handguard.

Running the AR57 suppressed was pleasant. It was hearing safe and I did not experience any gas to the face when shooting it suppressed. I would equate it to suppressing a .22 WMR round. Sound wise it is similar to shooting a .22wmr suppressed.

One issue with running a suppressor on the short 6″ barrel AR57 upper is how far retracted the barrel is. Yes I chose this option however trying to remove the suppressor can be difficult. At one point I was unscrewing the SpectreII off the AR57 upper and the threaded end cap seized up on the barrel while the suppressor unscrewed itself from the threaded endcap. As you can see in the photos above, there is not a lot of room to grab onto the sides of the threaded end cap to unscrew it. I had to use a flat head screw driver to turn the end cap. Only because of the shape and design of the end cap was I able to do that. If you had a different can rated for 5.7x28mm, like the Bowers USS 22 suppressor there is nothing to grab onto and it would be very difficult to remove it. The Bowers USS 22 does have interchangeable threaded endcaps so it would not be a huge loss to leave a dedicated end cap on the AR57 if you were to use that suppressor. Otherwise I would recommend getting another suppressor to be dedicated to this weapon system if you can afford to do so.


One thing that surprised me was how short the AR57 was with the SpectreII suppressor. It is as long as a P90 with suppressor.



Some of you may be asking: “Why do you have a PMAG inserted into the AR57?”. It is actually a brass catcher. Just like the P90, the AR57 ejects the spent brass downwards. You do not need to use an AR magazine but it is nice to use as a brass catcher. Only problem is that you need to permanently modify the magazine.

You need to remove the follower and spring from the magazine so that the empty brass can fall into the mag body. You also need to chop off the feed lips so the magazine can insert properly and engage with the magazine catch. Since the rounded feed lips are removed, you need to depress the magazine release button to insert the modified brass catching mag. Otherwise the edge of the magazine will hit the magazine catch and you can’t insert it further.



I chose a PMAG Gen 2 for a fundamental reason. The base plate and dust cover. Most magazine base plates are locked in place due to a spring pushing a floor plate down onto the base plate thereby locking it in place. With the magazine and follower removed there is nothing to keep the base plate from sliding off the magazine. That is where the Gen 2 PMAG steps in. The dust cover can attach and lock onto the bottom of the magazine to keep the base plate from coming off.

I was able to shoot a full 50 rounds without malfunctions and the modified PMAG contained all 50 pieces of spent brass. I will say this though, the 5.7x28mm is a very dirty round. A lot of carbon residue is blown downwards and into the magazine brass catcher.

IMG_3269 IMG_3270

The AR57 came with a new 8oz buffer which you replace your existing carbine buffer in your AR lower. Then it is a simple matter of replacing your upper receiver with the AR57 upper receiver. I did have issues of tolerance with my Troy Defense billet lowers. I could not get the AR57 upper to fit onto my Troy lowers. So I ended up using my Salient Arms International lower receiver. While the SAI lower is also billet it was able to fit the AR57 upper.

Aside from compatibility issues with my Troy lowers, The AR57 upper has a couple quirks. The magazine catch works but does not seem to engage the magazine completely. And when the side levers are pulled to release the mag catch, the catch protrusion does not seem to retract all the way so inserting and removing the magazine takes a bit more effort than I would like.


Magazine catch deployed.


The AR57 has a folding non-reciprocating side charging handle. It is on the right side of the receiver.



I prefer to have side charging handles on the left hand side. Now the AR57 upper appears to have a mirrored slot on the right side to allow for the charging handle to be installed on the left. But as you can see below, the AR bolt catch/release gets in the way. I suspect that if you removed the bolt release, then you could run the charging handle on the left side.



The AR57 upper works great but it is still not as cool as a select fire P90. Click on the Instagram video below.


I like the way the gun is setup except for side and bottom picatinny rails. I would rather see 57Center update the handguard design and go with MLOK. I believe it would greatly reduce the weight of the upper receiver and modernize the look a bit. There is no need for so much picatinny rail on the sides. Also by opting for an MLOK hand guard design it should be easier to machine and be faster to manufacture.

The AR57 upper retails for $745.99 on The upper receivers do not come with a P90 magazine so make sure you order one. I did not know this so I had to call around to my local gun stores and had to go buy one. Not a deal breaker, just a little annoying. I did not see this mentioned on their website and I think they should have it posted up to inform customers.

Nicholas C

Co-Founder of KRISSTALK forums, an owner’s support group and all things KRISS Vector related. Nick found his passion through competitive shooting while living in NY. He participates in USPSA and 3Gun. He loves all things that shoots and flashlights. Really really bright flashlights.

Any questions please email him at


  • thedonn007

    What advantage does this offer over a short barrel 5.56 upper? Is it mainly for the 50 round magazine?

    • Joe

      With a 12″ barrel 5.56mm has superior range, energy, and reload speed.
      5.7mm has 40% more capacity and lower recoil, but that’s about it.
      I see the tradeoff to get into a P90, but for AR platforms I just don’t understand the draw.

      • thedonn007

        That is what I am thinking as well. I have been very close to buying a PS90 over the years, but never pulled the trigger on it. As far as the added capacity of the 50 round magazine, you could use a drum or quad stack mag for 5.56. I realize a quad stack or drum magazine is not as handy as the 5.7×28 50 round magazine, but at least those options are available. Also, the mag changes for 5.56 AR magazine looks to be a lot quicker than the 5.7×28 50 round magazine.

        • Anomanom

          True, the mag switch on a P90 mag is slower than a regular AR mag, but you have to do it less often, so i suppose that’s the trade-off. It takes longer to changer the mag, but you get 50 instead of 30.

      • Anonymoose

        It seems to me that if they strengthened the fragile guns that they stuck the 5.7 in, they could load the round hotter to the point where you could get near-Commando velocities with a 55gr bullet from a 10″ barrel, and keep the compactness and short action length. When you shoot a .223 from a 10.5″ you are wasting a lot of potential there. Unfortunately they designed the 5.7 to be a pistol round and not a rifle round.

        • Giolli Joker

          It is even designed to run in blowback guns.

        • valorius

          Elite Ammunition loads the hot ammunition of which you speak.

          Such as a 28gr .85″ OTM spitzer at 2450 fps from the five seven pistol, or 3100 fps from a 16″ PS-90.

          • Anonymoose

            28gr is not what I’m looking for. I’m talking about 40gr+ ammunition. 28gr at the same velocity as .223 that is twice as heavy is not going to have nearly the effect on target that is needed for a duty weapon. Have gun with groundhogs and rabbits, though.

          • valorius

            The round im talking about is 28g cause it’s a hardened aluminum spitzer. Were it made of lead it would probably be about 45gr.

            Blows right through a IIIA vest, the jacket breaks apart and fragments, and the tumbling core continues on through gel to a depth of 12+%.

            That’s way more than “Groundhog” medicine.

            Lots of videos on you tube of hogs going down fast from 5.7

    • Otm Shooter

      You can shoot it with your .22lr can.

      • Nicholas C

        Not all 22 cans are rated for 5.7.

        • Otm Shooter

          Many modern 22 cans are, such as your Spectre II. I doubt most of the aluminum 22 cans are rated for 5.7.

          • Nicholas C

            Exactly which is why I was intrigued by the AR57 since my Spectre II can. But there are a lot of 22 cans that are not rated for 5.7

        • thedonn007

          You beat me to it, that was going to be my reply as well.

    • valorius

      5.7mm carbines have literally no recoil at all. A 10.5″ AR under rapid fire definitely recoils.

  • dave

    very cool post. i dont think id consider a scope or magnification past 3x since 5.7×28 loses much of its steam around 200m.

  • Will P.

    Accuracy? Reliability?

  • zack991

    Who in their right mind is going to downgrade the lethalityof their AR for a just cool factor, that you gain nothing but a more expensive around, a less lethal round for a carbine, and a high probability of more malfunctions. Make that magazine work with 5.56 and you will sell them, this is nothing practical what so ever.

    • thedonn007

      The overall length of 5.56×45 is 17 mm longer than 5.7×28, that would make it quite difficult to use the same magazine.

      • Anomanom

        I think he means making a 5.56 magazine that uses the same configuration of perpendicular round storage in a horizontal, top-mounted magazine.

        While it is a good design, making an upper that is compatible with the AR-type lower would be challenging, since it would require a gas system, unlike the 5.7x28mm. Maybe a short stroke piston, mounted at 45 degrees below horizontal like the Steyr Aug would work and allow downwards ejection. It certainly wouldn’t be compatible with standard forends though.

        • Jwedel1231

          Why not just mount the gas system below the barrel?

    • mechamaster

      Well, actually it is has it’s own merits.
      For anyone who want to enjoy the 5,7x28mm and the P-90 magazine without buying the P90 / PS90 ( or when it’s unavailable ).
      But still prefer the AR ergonomics, modularity, customizeability, nice trigger, and the familiar muscle memory.

    • Anonymoose

      The P90 mags actually are kinda crappy, or at least HK marketing would have you believe that.

      • Evil_Bonsai

        Well…if HK would ever deign to sell their coveted 4.6×30 in a platform available to us plebes, I’d start believing their marketing.

      • Kefefs

        So HK’s still upset NATO wanted to standardize 5.7×28 over their 4.6×30?

        • valorius


      • valorius

        my father has a P90, my brother did too. the mags arent an issue, as far as they will tell you.

    • Evil_Bonsai

      Downgrade their AR? You mean like shooting 9mm or 22LR or .40 S&W or…

    • Cymond

      Higher capacity, less recoil, easier to suppress, much shorter overall length when suppressed.

      I do think it loses more than it gains, but on the other hand, I would hate to pull the trigger on a 5.56 SBR indoors.

    • valorius

      Some types of 5.7mm tumbles and fragments on impact, just like good AR ammo does. And you can fire VERY small groups VERY fast with it (think a lightning fast one hole triple tap at civilian combat ranges).

      Trust me, you dont wanna get hit with a 5.7x28mm firing good ammunition.

  • LazyReader

    I’m just waiting for them to invent a p90 style fed rifle, COD did it

    • Secundius

      Unless you plan to live out the Rest of Your Life in Virtual Reality, THAT’S the only way your going to own one

  • dootdootbeep

    Is he shouldering an arm brace? Zomg call the ATF!

    • thedonn007

      Is it on his shoulder or his chest?

      • Otm Shooter

        ^ is he a cop?

        • thedonn007

          No I am not, just trying to be a smartass.

    • Nicholas C

      Actually it is a trick of the lighting. I am deliberately cheeking but NOT shouldering.

    • Otm Shooter

      You a cop?

      • dootdootbeep


        • Otm Shooter


  • Otm Shooter

    That’s pretty cool about using a mag as a brass catcher. I was not even remotely interested in these until I saw that. Thanks!

    • iksnilol

      IT’S LIKE A MACHINEGUN REVOLVER! No cases to trace. And the weaker 5.7 ammo makes it seem like the target was hit with 5.56 at farther distance.

      • Stan Darsh

        I believe some company offers 5.7 ammo loaded with M193 55gr bullets.

        • valorius

          Elite Ammunition does.

  • Mike

    I own a 5.7 pistol. Still waiting for proof of how effective the civilian ammo is

    • iksnilol

      That guy in the Fort Hood shooting used one without problems.

      Morbid example, but still, I wouldn’t underestimate 5.7 lethality.

  • BrandonAKsALot

    Definitely several more firearms chambered in 5.7×28 than the FiveSeven and the P(S)90.

    • iksnilol

      You got those MPA pistol/carbine thingamajigs.

      • BrandonAKsALot

        Some bolt actions as well. I believe even Savage offered one.

    • Secundius

      Johnson 5.7 Spitfire in M1 Carbine configuration, good to about 650 to 700-meters…

  • Lou

    I have one in 16″ and agree, very pleasant to shoot, very good quality, low recoil and accurate but slow to swap magazines and because of this, its not a defensive gun in my opinion. Plus its the same length as a standard CAR-15 or M4 with the 16″ barrel so you might as well just run 5.56 for defense as the original concept for the P-90 in 5.7 was to have a compact weapon which could easily pierce soft body armor unlike normal pistol rounds in an SMG. Ammo isn’t cheap either and too small for me to bother with reloading.

    Also, I have had to file aftermarket magazines to get them to lock up properly and some 5.7 rounds which have the Nosler-type plastic inserts have to have the tips snipped off or they get stuck in the magazine.

    It is the perfect weapon if you are attacked by an army of groundhogs though!

    • valorius

      you dont think its a defensive gun because the FIFTY ROUND magazine takes a few seconds to change?

      Where do you live, Mogadishu?

  • nova3930

    Kinda like to have one to throw on one of my SBR lowers but 750 is a little steep I think….

    • Jwedel1231

      Still cheaper than buying a Five-seveN or a PS90 + $200. Especially since you can get a short upper for your SBR lower. I need to get my lower SBR-ed so I can join the cool kids.

      • nova3930

        True. I could get one of the 6″ and swap it on my 8″ 300 lower with the troy PDW stock. Get something just as stupid short as possible, even with my spectre II mounted lol

        • Jwedel1231

          I’m going to have a shortened, suppressed rifle one of these days. Probably not for a few years, but I will eventually.

        • Nicholas C

          Don’t think it will work with the Troy M7A1 PDW stock since those use a proprietary Bolt/Buffer. However if you have the new Troy Tomahawk that allows the use of any bolt from what i can tell.

          • nova3930

            that’s an interesting point. if I did get one I have two other sbrs with normal buffer tubes so I’d have a backup plan…

  • livingonenergydrinks

    Give me an upper that accepts P90 mags that work with 22LR and you can take my money.

    • Nicholas C

      You can get a High Tower Armory 90/22 stock kit to turn your 10/22 into a P90. It has a faux P90 mag with .22lr in it. But it doesn’t feed the gun. It just stores extra ammo.

  • Harry’s Holsters

    The only practical purpose I can see for this is a defensive rifle for a small or weak person.

    • Jwedel1231

      Or for use indoors. Ever touch off a 5.56 inside a house or bedroom?

  • Jwedel1231

    Wow, thanks for putting this up. That is concerning.

    • Anon

      You’re welcome, I thought that everyone should know about that, because that’s a damn good reason to be concerned.

      I mean seriously, how do you screw up that badly?

  • Christian Hedegaard-Schou

    5.7 isn’t dirty.

    It’s just that the P90, 57 upper, and FiveSeven pistol are all blowback designs.

    It’s one of the fundamental flaws of the cartridge and those platforms (in my opinion) and is what makes reloading for 5.7 dangerous and not recommended.

  • VF 1777

    Gotta say it looks pretty damn cool!

    But I guess for me at least, it wouldn’t be a practical expenditure to deal with all of little oddities (and incur all of the expense) just to shoot 5.7 (over 300 BLK, 5.56 or even a PCC).

    One question — what would happen if it got turned sideways or even upside-down with all that brass in the ‘mag-brass-catcher’? Would it go back up into the weapon and cause and ‘issues’?

    • Nicholas C


  • Nicholas C

    Ahh. Did now know about that one. Thanks

  • ozzallos .

    I’ve only been seeing the 16in version of this and thinking what’s the point until seeing this article Well, duh. SBR it, of course. The Pmag brass catcher was a novel idea too 🙂

    Oh, and carbine in 22tcm plz thnx.

  • Mr. C

    But if you are one of the lucky people that own a select fire m16 lower, you now have a fully automatic 5.7……..

    • jcitizen

      Depends – some Title II registrations were caliber specific – so you could be in violation for putting this on the registered lower. I haven’t cross checked with the GCA ’86, but it could be that rule is for new manufactured non transferable guns – feel free to correct me on that.

  • jerry young

    I’m not sure about the empty mag brass catcher, it and doesn’t look like it would hold as many spent cases as the mag holds rounds, it just seems like a jam waiting to happen and now you have to not only change out mags but empty the brass catcher at the same time, I use a Caldwell mesh brass catcher on my AR’s they hold about 100 cases before needing emptied, something like that would seem a better option installed on the bottom of the mag.

    • Nicholas C

      It holds more than 50 rounds. You could sacrifice a Surefire 60 rd mag or a Magpul 40rd mag to hold more brass.

      There are brass catchers for P90s and some people have added brass catching nets to the bottom of their AR magazine.

  • valorius

    masterpiece arms makes a mac-10 based 5.7mm carbine, that uses Five Seven magazines as well.

  • valorius

    I ALMOST got a thompson center contender custom built in 5.7mm, just of the coolness factor alone.

  • valorius

    5.7x28mm is nasty stuff. Elite Ammo S4M OTM ammo fired from my five seven defeated every type of IIIA vest i tested it against (One each from US Armor, Safariland, and Second Chance)

  • John Yossarian

    Solution to a question that was answered by a SureFire 60 round magazine in an SBR

  • freewillyism

    shades of STARGATE (later episodes)!!!!

  • freewillyism

    xcellent forums Nick – keepem coming!!

  • freewillyism

    Are there loders for the mags!! I have a vietnam era USAF M16 – any thoughts on function issues???

  • One correction: Masterpiece Arms makes a 5.7 pistol from an uzi clone. Heavy as a small planet, but uses the FN5.7 30 round Magazines. Also, I’ve been modifying my 57 upper into a bullpup. Lost thebuffer tube and correcting that damn magazine catch… I’ll make these corrections available to 57 center when I’m done…

  • John Cheek

    WHY? If they wanted to fire 5.7 ammo in an AR15, why not just follow the protocall like 300BLK? Run the 5.7 ammo in ar15 “type mags” and change the barrel .

  • Secundius

    Just Exactly what Function Does the Lower Magazine Serve? A “Brass Catcher”!

  • jcitizen

    Who is PW Arms? Supposedly that was who was named as the manufacture of my AR57 upper. The markings are identical to the one in the article, however. Something is out of spec on it, because the 1st round bulges and won’t eject. With dynamics the way they are, I’m not ready to say the chamber is that far off. I used factory FN ammo, and the buffer inserts that came with the upper, so if that is the problem, it wasn’t my fault. I’m still trying to find out who to send it to.

    I’ve used one of these before, and it was fantastic. – no function problems at all. Used to literally put cases of ammo through it. Made one heck of a prairie dog rifle!! So to me it is worth finding out what is wrong with it. As far as the magazine catch, they’ve always been that way. I learned a trick on twisting it into battery, but have fallen out of practice – will have to revisit that if and when I ever get this upper fixed. I should have kept the original one I had, and never traded it off. I bought this in 2013, during the panic, so they may have been in a hurry on the production line.

    • Secundius

      PW Arms, is a subsidiary company of Technicki Remont of Bratunac, Bosnia. Which was founded in 1925, NOT a Big Company, Workforce base is ~500 employees…

      • jcitizen

        Guess I’ll have to rely on AR57 Central then. :/