Florida-based Diamondback Firearms announced their new DBX 5.7x28mm pistol earlier this year and the neat little gun is now filtering out to the market. 

Teased at SHOT Show earlier this year when the gun was in pre-production, the large format pistol uses an adjustable dual gas piston action-- no buffer tubes here-- with a stainless steel 8-inch threaded barrel that ends in the company's DBX series muzzle device. Using receivers crafted from 7075 aluminum and an M-LOK-compatible 6061 aluminum handguard, the gun is light, coming in at the 3-pound mark on our scales right out of the box. 

With the Honeybadger fracas, Diamondback is currently shipping the DBX bare bones with just the pistol, a detailed full-color manual, trigger lock, and a single Pro Mag (FN pattern) 20-rounder.  (All photos: Chris Eger/Guns.com)

Overall length, sans any accessories, is 15.25-inches while height is 7.3-inches. 

The pistol is very well balanced and feels extremely light, even for being over a foot long. 

Semi-auto with a locked-breech action that uses a dual gas piston, the latter is meant to be easily adjustable at the user-lever. Factory-set for the company's test ammo, it can be tuned to raise or lower the amount of gas that is bled into the two piston chambers to accommodate the increasing field of 5.7mm loads now on the market. This comes in handy when suppressed. 

The four-position pistons can be adjusted while the-- unloaded-- firearm is fully assembled with a flat-head screwdriver and the numbered gas settings are visible through the sight windows on each side of the handguard on the left and right. Not cycling reliably with your load? Dial it up to a higher number. Hard recoil? Dial it down. Easy peasy. 
5.7x28, left, and 5.56 NATO, right. The 5.7 was developed in the 1980s by FN for use in the P90 PDW and the Five-seveN pistol using bullets in the 20-to-40-grain range.
One benefit of the 5.7 is weight and size, with a full 20-round FiveSeven-style mag only hitting the scales at 7.4-ounces. In other words, just under a half-pound. 
The one-piece aluminum handguard is hard coat anodized and M-LOK compatible with five usable slots on both the left and right as well as three bottom-facing slots. 
The 1:9RH twist stainless steel barrel ends in a distinctive pronged brake/muzzle device. 
The triangular bolt-catch lever is above the mag well. The reciprocating charging handle is user reversible from left to right. 
The 7075 aluminum receivers are also hard coat anodized with ergonomic surface controls including a two-position AR-style safe/fire selector oriented to the left and a reversible side-charging bolt handle. 
The oversized magazine release is on the right and is easily actuated. The magazine drops free and doesn't have to be "rocked" in or out.
The DBX uses a standard AR-15 mil-spec trigger, which opens it up for easy upgrades. The pistol grip is a very functional hollow bottomed Magpul MOE K, another easy upgrade. Note the rear Picatinny rail for braces or other accessories.
The DBX fits in-line with Diamondback's AR-10 and AR-15 pistol offerings but is by far much more compact. 
Sure, it isn't as compact as, say a G19, but you get what we mean. This is where we point out that the weight difference between the G19 with 15+1 rounds of 9mm and the DBX as shown, with 20+1 rounds of 5.7, is only about 12 ounces. 
As the DBX ships sans sights, we added a Sig Sauer Romeo 5, a popular and affordable 20mm 2 MOA red dot that only weighs 5-ounces and leaves room for BUIS. 
The DBX is a flat-top with an 11-inch Picatinny rail that is ready for either optics or irons-- or both-- with a nice sight radius for the latter. Note how trim the pistol is, coming in at just 1.75-inches wide with about half of that being bolt knob. 
We also chose to upgrade our T&E DBX with an SB Tactical TF1913 stabilizing pistol brace, a sweet little triangular foldy boi 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
The TF1913 is 9.5-inches long and, when extended, brings the overall length to 24-inches. 
In the folded position, the TF1913 still clears the bolt knob and adds under an inch the total length, still allowing easy storage or stowage. Note the rear port on the receiver for a sling attachment point. 
Total weight with the Romeo5, TF1913, and 21 rounds of FN SS197SR V-Max comes out to a satisfying 4.4-pounds, which is still balanced enough to fire one-handed with ease. 
We've been testing the DBX with both the Pro-Mag and FN-standard 20-rounders, and it should be noted that aftermarket 30-round sticks are available. Spoiler alert: the FN mags are more reliable
The muzzle is threaded 1/2x28TPI, which is pretty common, and the lane gun at SHOT Show earlier this year carried a long-configured full-auto-rated SilencerCo Switchback 22 can. 

MSRP on the Diamondback DBX is $1,125. 

How does it shoot? More on that in a couple of weeks after we put some further range time into it, so check back for updates but the initial takeaway summed up in a single word is: gentle.

The Diamondback DBX
revolver barrel loading graphic