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Breaking Down the Diamondback Firearms DBX57 PDW

You’ve heard of Diamondback Firearms. For many, the name brings forth visions of cheap .380 handguns you may find in a purse. And Diamondback intends to change that. Sure, they make ARs too, but everyone makes an AR-15. So when someone told us we should check out their new Diamondback Firearms DBX57 PDW, we were skeptical. Cue our surprise.

The initial design goal was to create a PDW-style firearm that was lightweight and slimmer than any of the competitive offerings on the market, while demonstrating the newer, more serious level of Diamondback Firearms.

Adam Walker, vice president of engineering for Diamondback Firearms, told us the biggest challenge of the DBX was figuring out how to deal with the short-impulse of the 5.7mm ammunition while maintaining minimal mass in the reciprocating components. 

Diamondback Firearms DBX57 PDW
Out of the box, the DBX57 is just over 15 inches long.

FEATURES & DETAILS

There are no two ways about it — the DBX is really tiny. With an 8-inch barrel and an overall length under 16 inches, the barrel of a standard AR alone is longer. And it weighs 3 pounds naked. 

If you gave the Diamondback Firearms DBX57 a quick glance, you’d probably assume this was based on an AR. And in some ways that’s true. The DBX has an upper and lower receiver machined from billet 7075 aluminum, held together by two takedown pins. And a lot of AR parts are compatible with the DBX, including those pins. The DBX accepts AR triggers, muzzle devices, grips, and safety selectors. 

The reciprocating charging handle can be swapped to either side and is angled downward to keep your knuckles from scraping on the optic. We’d prefer it to be a scootch longer, but it wouldn’t be difficult for an aftermarket company to produce them. 

The rear of the lower receiver has a Picatinny rail to accommodate a great number of stocks or braces on the market. Additionally, there are five staggered M-LOK slots on either side of the removeable handguard, and three on the bottom. 

The Diamondback Firearms DBX uses FN Five-seveN pistol magazines (ours shipped with two 20-round ProMags), which while still relatively rare on store shelves are increasingly available online.

DBX57 PDW
A SureFire XVL2 gives us a bevy of visible and IR options with a tiny footprint.

There are some functional differences between the preproduction unit we got handsy with at SHOT 2020, namely the addition of a bolt lock and release, magazines that lock back on empty, and the adjustable gas system. Instead of an AR-type bolt release, Diamondback Firearms uses a catch reminiscent of the CZ Scorpion EVO 3. 

Something that really stands out about the Diamondback Firearms DBX57 is that it uses not one, but two gas pistons. Though we’ve seen this before on the Remington Versa Max-based TAC-13 shotgun (see RECOIL Issue 42 for a full review) it certainly couldn’t be called common. However, unlike the Versa Max, which uses hull length to determine gas pressure, the DBX requires manual adjustment, and both settings have to match for proper function.

Walker tells us, “The requirement for each piston cap to have its gas setting selected independently was done solely to reduce complexity of the system. We had designed a version that used interlocking gears to ensure that the settings were always synchronized, but it was too costly and required some of the components to be enlarged, which worked against our main design goals.”

The pistons are adjusted from the front of the gun with either a Phillips or flathead screwdriver; there are no detents to push in first. The settings are visible through a port on either side of the receiver, so if you plan to paint your DBX, take care to mask off that area. 

diamondback firearms

DISASSEMBLY

Don’t let those takedown pins fool you — stripping down the Diamondback Firearms DBX57 is significantly different than an AR-15. It’s different enough that we ultimately had to watch Diamondback’s instructional video several times — and we don’t normally read manuals. 

The lower receiver is like a standard AR. Swap your triggers and selectors as normal. Note that the rear takedown pin spring and detent are secured by the pistol grip like the selectors. The lower handguard is held in place by the front takedown pin. However, since the handguard uses some pre-tension to remain in place, a non-marring punch and light hammer makes the job much easier. 

diamondback firearms DBX57

After separating the receivers, the handguard can simply be slid forward. Before removing the recoil spring assembly, you have to manually lock the bolt to the rear and remove the charging handle. Only then can the recoil spring assembly be removed. 

The next step will feel like you’re about to break something. You have to wiggle out the entire barrel assembly, recoil spring, and bolt carrier. Take some care not to lose the bolt hold open or the small spring, or you’ll be crawling around the floor with a flashlight like you just lost the front detent spring on an AR.

Reassembly is the reverse. It takes a bit of finesse to take the barrel assembly in and out, so we suggest you try it a few times first. This isn’t quite Ruger MkIII territory in terms of disassembly, but it certainly isn’t an AR. 

OUTFITTING

Because the Diamondback Firearms DBX57 can use standard AR triggers and selectors, it seemed like a waste not to take advantage ourselves. The trigger is a Midwest Industries C trigger, which is a curved single-stage 3.5-pound drop-in complete with anti-walk pins. The selector comes from Battle Arms Development and is their BAD-ASS-PRO reversible ambidextrous safety, which allows for a shorter 60-degree throw. Irons are the easy-button Magpul MBUS Pro.

Since we’re really talking about a PDW role, we wanted an optic with an extremely wide FOV. The answer came in the form of a new EOTech XPS3-0. For a weapon-mounted light, we decided to keep it small and handy, deciding on a SureFire XVL2-IRC, which has both white and infrared light output as well as both green and infrared lasers. You can configure the XVL2 for different combinations of visible or IR use. It’s not the brightest per the lumen cults, but it’s small and incredibly versatile and, importantly, viable within the anticipated range of a PDW.

dbx57 trigger internal

Something that must be noted is that the barrel diameter of the Diamondback Firearms DBX57 is too narrow to provide a workable shoulder for your muzzle device, which is also an issue with the FN SCAR. For a brake or a flashhider, that isn’t a deal breaker, but if you want to use a silencer not just any old device will do. In this situation, you should ideally use a device that indexes from the muzzle itself, such as the Dead Air SCAR flash hider. In order to accommodate a standard SureFire WarComp, we used a locking nut to circumvent the shoulder issue — and made damned sure to check alignment with a precision rod before firing.

There are an awful lot of .22LR silencers out there that claim to be “rated” for 5.7x28mm ammunition, but what that mostly really means is just that they’ll survive the use of 5.7mm; a smaller Kurz-sized 5.56 silencer will usually perform much better. In our case, we went with a SureFire SOCOM556-MINI2 we had on hand. 

Since this is configured as a pistol, we affixed a folding JMAC Customs AB-8R Arm Bar with a Tailhook brace attachment.

AT THE RANGE

Due to the current ammo crunch, we couldn’t test all available ammunition with the Diamondback DBX, instead using some Federal American Eagle 40-grain FMJ ammo we had in inventory. While ammunition selection is still limited, due to the recent increased interest, there are more options, including new JHP defensive loads from Speer. We look forward to further testing in the future. 

Even fully loaded up with an optic, light, and silencer, the DBX is lightweight at just below 6 pounds; pop the can off and you shed another 15 ounces. It’s well balanced and handles with ease. The recoil of the DBX is far easier to control than the bottleneck round would otherwise tell. A simple blowback 9mm has significantly more recoil than the DBX. Controlled pairs and longer strings of fire were incredibly easy to control. 

diamondback firearms DBX57

We had 300 rounds of Federal available, and all went through the pipe without issue, both suppressed and unsuppressed once we got our gas dialed in.

Five-shot groups at 100 yards were 1.25 MOA, which is frankly better than we expected from the short barrel of the DBX. If you’re using the DBX at PDW distances as anticipated, you’ll be just fine.

LOOSE ROUNDS

If you even just glance through this issue, you’ll see several companies reinventing themselves. For over a decade, Diamondback was seen as a company that would forever be making Kel-Tec clones. Since those early days Diamondback expanded into the world of the AR-15, and more importantly, have been spending time on guns that are truly their very own. The DBX proves they can stretch much further outside themselves than anyone else thought previously. 


Diamondback Firearms DBX57

Caliber: 5.7x28mm
Capacity: 20, 30
Barrel length: 8 inches
Overall length: 15.25 inches
Overall Height: 7.3 inches
Weight (Unloaded):3 pounds
MSRP: $1,125
URL: diamondbackfirearms.com

Accessories:
Ascend Armory Foregrip: $40
BAD-ASS-PRO Selector: $45
SureFire WarComp: $149
Magpul MBUS Pro: $189
Midwest Industries C-Trigger: $150
JMAC AB-8R Brace & Mech: $240
EOTech XPS3-0: $675
SureFire SOCOM556-MINI2: $1,079
SureFire XVL2-IRC: $1,349

Price as configured: $5,041


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