Mossberg was one of the first innovators within the “non-NFA, shotshell-firing firearm” space with the introduction of its pump-action 590 Shockwave in 2017. The hallmark of the design was its bird’s head grip configuration, which allowed the firearm to be equipped with a shortened 14.5” barrel while remaining at an overall length of just over 26”. Soon after, several other companies followed with variants of this non-NFA design, including some semi-automatic models. But Mossberg stuck with its pump-action Shockwave until 2025, when the company released its semi-automatic 990 Aftershock. Watch our “Gun Of The Week” video above to see the 990 Aftershock in action on the range.
Like the 590 Shockwave, the Mossberg 990 Aftershock makes use of a Shockwave Technologies bird’s head grip, paired with a shortened, 14.75” barrel. Chambered for 12-ga. shotshells, the under-barrel tube magazine has a capacity for up to five 2 ¾” shells. The semi-automatic mechanism of the 990 is gas-operated, with propellant being tapped off the barrel and directed into a gas cylinder, where it pushes a piston rearward, thereby driving the bolt to the rear of the receiver. An action-return spring wrapped around the magazine tube returns the bolt into battery, which chambers a fresh shotshell as it travels.
In terms of controls, the 990 Aftershock borrows many elements from existing Mossberg designs, notably the 940 line of semi-automatic shotguns. The ubiquitous top-tang safety selector is found centrally at the rear of the aluminum receiver, but it has been widened and made easier to operate, thanks to feedback from outdoor professionals. An oversized, knurled charging handle is located on the bolt, allowing operators to manually charge the gun. A bolt release is located just beneath the ejection port, and it is partially protected by a gate to prevent unintentional activation.
Other features include a well-fixed strap located on the underside of the textured fore-end that provides greater control during firing, as well as M-Lok attachment slots located on either side of the gun just behind the muzzle, providing an easy mounting point for a light or laser. A drilled-and-tapped receiver accommodates a Picatinny rail for mounting optics, but a fiber-optic front sight is also included.
Part of the benefit of the 990 Aftershock’s operating system is that, unlike the original Shockwave design, the semi-automatic mechanism absorbs some of the energy of a fired shotshell, which softens the recoil impulse, compared to the locked firing system of the pump-action Shockwave. This provides additional control, and when combined with the self-loading semi-automatic operating system, it means that this platform offers much more rapid follow-up shots.
Our range experience bore out the benefits of this fast-firing mechanism, and our testers felt that the Aftershock was a supremely capable platform for close-range personal defense. Its compact dimensions also make it ideal for use within tight confines, such as the inside of a house. Given the short-range case use for an arm like this, its semi-automatic operation makes it supremely practical, and its non-NFA configuration means it’s that much less complicated to own and use. For more details, visit mossberg.com.
Mossberg 990 Aftershock
Manufacturer: O.F. Mossberg & Sons
Gauge: 12; 3″
Action Type: gas-operated, semi-automatic firearm
Stock: polymer Aftershock bird’s head-style grip
Receiver: aluminum, hardcoat-anodized finish; drilled and tapped for optics
Barrel: steel; matte-blued finish
Magazine: tubular; five-round
Sights: red fiber-optic pipe
Trigger: single-stage; 4-lb., 14-oz. pull
Weight: 6 lbs.
Accessories: owner’s manual
MSRP: $1,120
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