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.

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.

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.

 

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 57Center.com. 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.