The handy DBX 57 pistol works well and fits a niche in the ever-growing category of innovative new firearms chambered in 5.7x28mm. 

Debuted by Florida-based Diamondback Firearms at the 2020 SHOT Show and soft released to the market last May, the DBX is a large format pistol that uses a dual gas piston action with an 8-inch threaded barrel that ends in a muzzle device. 

Equipped with a top Picatinny rail for optics, M-LOK slots for accessories, and a rear Pic rail for braces or stocks (NFA rules apply), the gun weighs 3 pounds flat and runs just 15.25 inches long overall, sans any aftermarket add-ons. 

The Diamondback DBX has rails and slots for just about any extra you can think of and – using receivers made from 7075 aluminum and a 6061 aluminum handguard – still comes in at 3 pounds, about half the chunk of an FN PS90. (All photos: Chris Eger/
When it comes to comparable sizes, the DBX splits the difference between a standard handgun and even a small AR-15 or AR-10 style pistol. 
The DBX ships with a single 20-round ProMag and a manual. 


Related: 3 Pounds of Awesome: An Overview of the Diamondback DBX 5.7




The DBX has a lot going on under the hood.

It has two user-adjustable gas pistons that can be dialed up or down with the aid of a screwdriver in the field without stripping the gun down. It accepts standard AR-15 triggers and grips while having the same style safety lever format. Unlike the AR, there is no buffer tube, and the locked-breech rotating bolt's action is side charging, oriented out of the box with a left-hand knob. But don't worry, it can be swapped to the right if that's how you swing. The barrel is threaded with a 1/2x28 TPI pitch, opening it up to a wide array of muzzle devices and cans.

As far as mags go, the DBX takes standard FN FiveseveN style double stacks, which are readily available in 10-, 20-, and 30-round versions both as FN-branded and aftermarket. 
Looking at a parts diagram of the DBX, you notice some very familiar AR-like items, such as the trigger group and safety selector, as well as some rather peculiar components such as the dual adjustable piston system. (Chart: Diamondback) 

With that being said, field stripping and maintenance of the DBX has a learning curve to it. Be sure to delve into the company's 48-page manual, which is online if you lose your printed version that ships with the gun, and take advantage of the series of six short, step-by-step instructional videos on Diamondback's webpage covering the gun.

All of this would seem to point to a gun that is on the buggy side, especially for a new design that was only in pre-production a year ago. However, we found that it chugged through 350 rounds of factory 5.7 ammo with two hiccups while using a ProMag aftermarket magazine. All rounds were fired fresh out of the box with no additional lube or adjustments, only a function check and a bore examination to make sure it was clear. The only other negative we could lob at it is that the bolt didn't always lock back on an empty mag, especially when dirty. 

We ran 250 rounds of Federal American Eagle 5.7x28mm, loaded with a 40-grain total metal jacket bullet, and another 100 of FN SS197SR, loaded with Hornady's polymer-tipped V-Max bullet. We'd have loved to put two or three times that amount through the gun, but the Great Ammo Shortage of 2020-2021 cut back on our availability. 

An interesting result on the V-Max was that we found it penetrated 13 to 15 inches of denim-wrapped 10-percent FBI gel provided by Clear Ballistics, shedding the polymer tip in the first few inches of that and producing a 9mm mushroom at the end. A hotter load, such as Elite Ammunition’s all-copper T6B or Speer's new 5.7 Gold Dot, should do even better. 

The V-Max ran about 14 inches on average in ballistics gel from the DBX while the American Eagle TMJs exited the 16-inch block and kept going. 


On the range


We upgraded our T&E DBX with an SB Tactical TF1913 stabilizing pistol brace, a great little triangular side-folder with a steel hinge that adds around 10 ounces to the gun. Such rails are increasingly common on pistols like the SIG MPX, SIG MCX, SIG Rattler, and Rock River LAR-PDS.

We also added a Sig Sauer Romeo 5, one of the best $100-ish 20mm 2-MOA red dots on the market. 

Total weight with the Romeo5, TF1913, and 21 rounds of V-Max came to 4.4 pounds, which is still balanced enough to fire one-handed with ease. You can move to 30-rounder FN mags and only add a couple of extra ounces. 
The rear of the DBX includes a QD sling point for those wanting to go that route. 

Recoil is negligible, even one-handed, as the gun's weight is comparable to a longslide M1911. 

With the brace, even more so. 

The brace, extended and strapped down, added a bit more control to a gun that is already smooth. 

And the gun in such a setup is easy to move back and forth with. 

Accuracy, even with the thin 1:9 RH twist barrel, was excellent, with the "cheaper" American Eagle TMJs clocking under two-inch groups at 25 yards when braced. 



The DBX, due to its lightweight and easy stowage, could make a good gun around camp or on the trail

The DBX could make a great survival or pack gun, as the 5.7 cartridge is just a skosh bigger than .22 WMR but still a lot smaller than a 5.56 NATO, meaning you can carry more ammo in the field per ounce. For instance, 50 rounds of .22 Mag weighs 6.4 ounces compared to 50 rounds of 5.7 at 12 ounces, while the same quantity of 5.56 hits the scales at 21.6 ounces. The most amazing thing I should note about this is I had 50 rounds of each one on hand to weigh!

From left to right, .22 Magnum, 5.7x28, and 5.56 NATO, each roughly doubling in overall cartridge weight

The gun balances extremely well, has virtually no felt recoil, and is both thin and lightweight, even while tricked out and loaded. I've handled heavier airsoft guns. This sets it up to be popular on the range with "kids of all ages" as they say, since it is just flat-out fun to shoot, especially with the right suppressor. Once the ammo situation returns to something approaching normal, the DBX could really shine as a range toy.

Speaking of ammo, if outfitted with the right load, the prospect of a reliable 3-pound PDW with 31 rounds on tap could sound good to many for a self-defense/home protection tool. 

Further, the DBX platform is so interesting that perhaps Diamondback will offer it in different chamberings. 

In the meantime, stand by as we stretch it out to a longer range and try it with a few more loads.

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