Diamondback DBX 5.7mm Pistol - Worth $1,000?

Enter, the Diamondback DBX

The Diamondback DBX is a semi-automatic, magazine-fed piston-driven firearm that looks like the result of crossbreeding an FN SCAR with an old Walther MPL submachinegun. But it's what's under the hood that really matters in this case.

The majority of large-format pistol-caliber firearms operate via direct blowback. Meaning, the action doesn't lock, and the bolt is only held closed by the tension of the recoil spring. To ensure the recoil of the action isn't too violent or premature, these firearms tend to use heavy bolts as a way of delaying the cycling of the bolt.

This is done primarily for two reasons: First, it works. It's very simple, relatively easy to manufacture, and even if the gun gets congested with carbon or debris, it will continue to function reliably. The other reason is cost. Direct blowback bolts and carriers tend to no require as much machining time as locked-breech designs simply because no precise camming surfaces are necessary. Another cost-saving aspect of this is that these guns normally don't have a gas tube and simply utilize the barrel itself to transfer some of the expanding gasses rearward to cycle the action.

The downsides of this method of operation are weight and disproportionate recoil. With a heavy bolt and stiff recoil spring, the reciprocating mass of the carrier group tends to amplify the recoil impulse as it moves towards the rear of the gun. With shoulder-fired weapons, this isn't as large of a concern, but pocket pistols like Walther's PPK can be relatively snappy and the stiff recoil spring makes the slide difficult to rack for shooters with limited upper body strength or arthritis.

Under The Hood

The Diamondback DBX takes a page from the SIG MPX's playbook and utilizes a short-stroke piston instead. Meaning a hole in the barrel siphons excess hot gas from a detonated round that drives a small piston against the bolt carrier group to cycle the action. (Similar to an MCX, MPX, or Russian SKS)

At the beginning of the recoil cycle, the bolt rotates a small amount, and its lugs cam against a matching recess in the chamber. Once it does so, the action is unlocked, and the bolt carrier group freely travels back against the recoil spring. Once fully back, the compressed recoil spring propels the carrier group forward chambering a fresh round, priming the hammer, and locking the bolt inside the chamber.

Sounds complicated, and in some ways it is, but the result is an incredibly soft-shooting firearm.

Neat, but so what? Well, this is an already uncommon setup for pistol caliber firearms, but exceptionally so for those chambered in 5.7mm; For several years every gun chambered in 5.7mm was exclusively direct blowback. But the recoil reduction and novelty of this aren't enough to sell most shooters on the gun alone, what about features?

Barrel

The DBX is loaded with several desirable features that demonstrate that the engineers are Diamondback weren't simply content to churn out a novelty gun in a semi-niche caliber. There are so many, that we'll just start at the muzzle and work our way back.

First off, the muzzle features a combination ported brake, flash suppressor, that reduces the already tame recoil of the round to an absurd level. Double and trip taps on targets are a breeze with the recoil of the DBX feeling just slightly more intense than that of a .22lr carbine.

Under this muzzle device, the barrel is threaded to standard 1/2x28 thread pitch, so shooters can install whatever AR-15 muzzle device they want - including sound suppressors. Speaking of which, while 5.7mm isn't a great round to suppress since it relies on velocity over projectile mass, most quality .22lr rimfire suppressors are designed to handle it. Meaning shooters who already own a rimfire suppressor can get more use out of their tiny, lightweight can. (Note: Not every 22lr suppressor can handle 5.7x28mm, check with the manufacturer before installing one.)

The barrel itself is stainless and features a medium contour that strikes the perfect balance between consistent accuracy and weight distribution. Continuing back, the DBX's barrel features an adjustable gas system that allows shooters to dial in the gun to their favorite suppressor allowing for the quietest operation possible. This can also be used to increase backpressure should the gun become fouled up or underpowered ammo is used.

Handguard and Upper Receiver

Around the barrel, the Diamondback DBX features an extruded-aluminum free-floated two-piece handguard. The lower portion features two arrays of M-Lok slots on the left and right, with a single set of M-Lok slots on the bottom.

The upper portion of the rail is actually an extension of the upper receiver itself and appears to be milled from a solid block of aluminum. This gives shooters a rock-solid monolith upper Picatinny rail for mounting optics, lights, or lasers that is certain to hold zero.

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