You've doubtless heard the expression that if it looks like a duck, walks like a duck and sounds like a duck, then it's a duck. The Mossberg Shockwave, though, with its 14-inch barrel and bird's head grip, looks very much like a Class 3/NFA firearm or maybe even a sawed-off shotgun, but it is neither.

So why is the Shockwave classified by the ATF as a “firearm” and available to shooters without having to buy a tax stamp or fill out paperwork? Mossberg found a clever way to legally manufacture the Shockwave without having features that require shooters to deal with reams of paperwork and pony up the expense of tax stamps.

The Mossberg Shockwave is built on the company's M590 receiver with a 14-inch barrel and an overall length of 26.37 inches.
How is the Mossberg Shockwave legal? It's built on the company's M590 receiver with a "bird's head" pistol grip, a 14-inch barrel, and an overall length of 26.37 inches, meaning it's a non-NFA firearm.author photo

The Shockwave is manufactured by fitting a shotgun-type receiver with a “bird’s-head” style grip in lieu of the shoulder stock, which is an important detail.

As part of the legal definition, a “shotgun” must be made to be fired from the shoulder. Since Mossberg fits a new receiver with a pistol grip at the factory, the Shockwave falls under the definitions in the Gun Control Act of 1968, which calls it a “Pistol Grip Only Firearm.” That’s why the Shockwave doesn’t fall under the National Firearms Act rules and doesn’t require a tax stamp.

These types of firearms can include certain shotguns having a barrel or barrels of less than 18 inches in length. Here’s the final reason why the Shockwave can have that short barrel: According to the NFA definitions of a “firearm,” the overall length must exceed 26 inches. The Shockwave, from muzzle to grip, measures 26.37 inches.

So, what seemingly looks like an NFA shotgun is actually classified as a PGO (Pistol Grip Only) firearm. Although some state regulations prohibit the sale of such guns (check with your state police), there is no need for the NFA stamp to legally own the Shockwave. No extra cost, no extra paperwork, no need to wait.

Ain't that ducky?

A close look at the Raptor grip, made by [Shockwave Technologies
A close look at the Raptor grip, made by Shockwave Technologies.author photo

Short and Sweet

Historically, Mossberg has offered the Model 500 and Model 590 shotguns in traditional upland and waterfowl hunting models, as well as in tactical variants that are factory-fitted with a shoulder stock and extended magazine. The minimum barrel length on these tactical shotguns is 18.5 inches. Some pistol-grip models, such as the 500 Cruiser and JIC (Just In Case) models, also have a barrel length of 18.5 inches and an overall length of well over 26 inches. None of these models require ATF paperwork since the barrel length is over 18 inches, and are perfectly legal to buy in any gun shop without a tax stamp or having to go through the wait and paperwork.

However, if the shoulder stock of a shotgun is replaced with a pistol grip that makes the weapon less than 26 inches in the length, the ATF classifies the weapon as an Any Other Weapon (AOW). These AOW firearms require a tax stamp, paperwork and wait time.

The Shockwave is different from them all. Its receiver is based on Mossberg’s tried-and-true Model 590 action, which is a workhorse of a shotgun action. Shoot a 590 in rain, snow, or dust, and the 590 keeps on shucking and shooting. I’ve tried to wear one out and haven’t come close to succeeding.

The forehand is coarsely ribbed polymer with a strap that secures the shooter’s support hand stays put when the Shockwave starts talking in birdshot, buckshot or slugs.
The forehand is coarsely ribbed polymer with a strap that secures the shooter’s support hand stays put when the Shockwave starts talking in birdshot, buckshot or slugs.author photo

Features and Controls

Shockwave Technologies created the finely textured polymer “bird’s head” grip, which is named the Raptor. The company also supplies the fore-end strap.

The Shockwave did not initially come with a sling swivel post. Based on initial feedback, Mossberg made a “running” production change on the 590 Shockwave, and a swivel stud, for ease of sling attachment, is now standard on the Shockwave.

Features are similar to other Model 590 shotguns, including the ambidextrous safety button located at the top rear of the aluminum alloy receiver. Both left-and right-hand shooters find that the thumb of their shooting hand falls directly on top of it.

The [OPSol Texas mini-clip](http://www.opsolmini-clip.com/) (top) is molded from a hard yet flexible polymer material that snaps into the loading port on the bottom of the Shockwave’s receiver (bottom
The OPSol Texas mini-clip (top) is molded from a hard yet flexible polymer material that snaps into the loading port on the bottom of the Shockwave's receiver (bottom).author photo

The Shockwave also has double action bars, so the slide pumps smoothly. The fore-end is coarsely ribbed polymer with a strap that ensures the shooter’s support hand stays put when the Shockwave starts talking in birdshot, buckshot or slugs.

The trigger housing is polymer and pops out of the receiver after removing two pins.

The 14-inch barrel is made with a heavy wall, like those on the barrels Mossberg puts in their military 590A1 models. A brass bead front sight tops off the plain barrel.

Capacity

One characteristic I noticed immediately about the Shockwave was that it has the same magazine capacity as a standard Model 590. When using 2-3/4 inch shells, capacity is 5+1. Load 3-inch shells and you lose a round; capacity is 4+1. What changes the capacity math are Aguila 1-3/4 inch minishells, those up capacity to 8+1 shells.

Using Aguila Minishells ups the capacity of the Shockwave from  5+1 with 2-3/4" shells to 8+1 shells.
The OpSol adapter ensure the short shells cycle reliably in a gun made for 2-3/4" or 3" shells.author photo

Those small shells produce bite with little recoil, but are notorious for not cycling properly in a shotgun's action. That's because nearly all 12-gauge repeater shotguns are designed to use a shell with a minimum length of 2-3/4 inches. The OPSol Texas Mini-Clip allows you to fire Aguila minishells reliably. Mossberg does not sell the Mini-Clip; it's an aftermarket product that can be purchased separately. Put this simple and relatively inexpensive adapter (about $15) into the gun and you'll get off nine shotgun rounds in a row.

The magazine capacity with 2-3/4 inch shells capacity is 5+1; with Aguila 1-3/4 inch minishells capacity increases to 8+1 shells.
The magazine capacity with 2-3/4 inch shells capacity is 5+1; with Aguila 1-3/4 inch minishells capacity increases to 8+1 shells.author photo

The OPSol Texas mini-clip is molded from a hard yet flexible polymer material that snaps into the loading port on the bottom of the receiver. Push the OPSol Mini-Clip in the loading port so it is flush to the rear and the bottom of the port. Rack the slide a few times to ensure the clip is in position. It can be removed just as quickly and easily without tools. The Mini-Clip reduces the size of the loading port so a minishell is perfectly positioned as it moves from the magazine tube to the elevator assembly. The Mini-Clip is compatible with all Mossberg 500, 590, and 590A1 models.

At the Range

With the OPSol Mini-Clip installed I placed an Aguila buckshot minishell in the chamber and stuffed the magazine tube with eight more. The buckshot minishell is loaded with 11 pellets: seven No. 4 buck pellets and 4 No. 1 buck pellets. They leave the muzzle at a respectable 1200 fps according to the factory so I assume out of the Shockwave the muzzle velocity is a bit slower.

In hand, the Shockwave evokes a sense of compact power. With my support hand held in place by the strap and my firing hand on the grip, the Shockwave cycled smoothly and loosely, like a Model 590. It’s highly maneuverable, as you would expect with a shotgun that measures a bit over two feet long.

The only issue with the Shockwave is how to shoot it. You can forget shooting the Shockwave one-handed unless you have biceps like a Navy SEAL. You will get one shot off, then you’ll need to cycle the action.

I used a two-hand hold with two different shooting techniques. One was to hold the Shockwave at eye level and use the brass bead to aim, similar to firing a handgun. The second—and the most satisfying—was to point-shoot from the hip.

I was surprised at how surgical the Shockwave was in action. A myth perpetuated about shotguns, especially a short barrel shotguns, is that they only need to be pointed in the general direction of the threat. Not true. Modern buckshot loads need to be aimed. When using a shotgun, and buckshot in particular, you must remember that you are responsible for all the projectiles in the shell. A missed shot or badly aimed shot could have consequences, especial in the confines of your home with other family members in the room down the hall.

The author experimented with using the Shockwave's brass bead to aim, similar to firing a handgun, and found it surprisingly accurate.
The author experimented using the Shockwave's brass bead to aim, similar to firing a handgun, and found it surprisingly accurate.author photo

At 10 yards, the Aguila buckshot minishell gave me a 10-inch pattern on average. Recoil was mild due to the grip and the weight. Aiming with the bead, I was able to get all pellets on an 18-inch wide piece of cardboard. Firing from the hip for speed, by bracing the grip on my hip and pumping as fast as I could, the Shockwave reeked uttered perforation on the target. Recoil was mild.

Next I loaded the Shockwave up with Aguila minishells loaded with 7/8-ounce slugs, and blasted eight holes while from the hip as if I had been training with the Shockwave for years. Aiming the slugs with the bead proved that the Shockwave was capable of good accuracy at 10 yards.

Then I removed the Mini-Clip and moved up the 12-gauge food chain to 2 3/4-inch Winchester military grade buckshot loads. Fired from the hip, but not braced against my hip, the pattern from the nine 00 buck pellets averaged a tight 4.25 inches. They produced more recoil, of course, but proved precise on target.

At 10 yards, the Aguila buckshot minishell gave the author a 10-inch pattern on average.
TheAguila minshell buckshot averaged a 10-inch spread at 10 yards.author photo

Moving up to a 3-inch shotshell means brutal recoil and a less fun shooting experience.

I reinstalled the Mini-Clip and burned through the remaining Aguila ammo as if it was coming up an expiration date. Powerful, brutal and surgical, the Shockwave performed with perfection. You need two hands on the Shockwave to cycle the action and you soon realize how the fore-end strap helps to keep your hand in position during rapid fire. You needed a screwdriver to remove the grin on my face after shooting the Shockwave.

While I have fired my share of exotic firearms, in reality most are too expensive, too difficult to shoot, and more of a novelty than a necessity. Though I think shooting the Shockwave should be on every shooter’s bucket list, I also see the Shockwave as a well-designed close-range defense weapon. Mine is loaded with 8+1 rounds of Aguila minishell buckshot and staged in my home. And while the Shockwave complies to the letter of the law, it won’t be complacent if evil ever breaks in your door.

Slugs and buckshot at 10 yards fired from the hip.
Slugs and buckshot at 10 yards fired from the hip.author photo

SPECIFICATIONS

Action: Slide

Gauge: 12

Chamber: 3-inch

Overall Length: 26.37 in.

Barrel Length: 14 in.

Choke: Fixed Cylinder bore

Grip: Shockwave Technologies Raptor Bird's Head, black polymer

Fore-end: Shockwave Technologies Raptor Strap Kit, ribbed black polymer

Sight: Brass bead

Finish: Matte blue

Weight: 5.25 lbs. unloaded

Capacity: 8+1 (1 3/4-in. shells), 5+1 (2 3/4-in. shells), 4+1 (3-in. shells)

Trigger Pull: 6.5 lbs.

MSRP: $455

Winchester military grade buck shot in 2 3/4-inch shells averaged a tight 4.25-inch pattern with the nine 00 buck pellets at 10 yards.
Winchester military grade buck shot in 2 3/4-inch shells averaged a tight 4.25-inch pattern with the nine 00 buck pellets at 10 yards.author photo