After playing with the Mossberg Shockwave for the first time at the last SHOT Show Range Day, I wanted one. Thanks to some enabling from my friend Brian M. I picked up a Mossberg Shockwave at a local gun store for $380 out the door. Not terrible.

I went with the Mossberg Shockwave because it comes drilled and tapped for an optic rail. Also I can use the OpSol mini clip for use with Aquila mini shells. Oh and the 590 shockwave was in stock. The Remington was not.

Here is the Mossberg Shockwave next to a Cheetah 12 shotgun that Brian was working on. He modified the Zhukov handguard to fit the Cheetah 12.

As you can see, the Mossberg 590 Shockwave is rather small in comparison. It is a perfect size for ATVs.

Specifications

• 12 Gauge
• Capacity: 5+1
• Choke: Cylinder
• Barrel Length: 14″
• Bead Sight
• Weight: 5.25 lbs
• Length: 26.37

Brian volunteerd to be a test monkey and test fire the Mossberg Shockwave. He grabbed some 3″ 9 pellet buckshot and some 2&3/4″ slugs. Thanks Brian for shooting those so I wouldn’t have to.

 

The 3″ buckshot was rather stout. We had difficulty controlling the handguard. It often slipped out of my hand. I found the strap to be too loose and did very little to help control the muzzle climb.

Brian’s neighbor Denny came over and he shot the 590 Shockwave one handed. When he shot it, the firearm recoiled back but the trigger guard hit his fingers and stopped the rearward travel. The pump grip kept traveling rearward due to inertia and auto ejected the spent shell.

 

Modifying the 590 Shockwave

I wanted to try the 590 Shockwave with a pistol grip and brace to see if it made shooting any better. I ordered an Ergo Grip adapter. For some reason it was not clear all the way through for the mounting screw so I fixed that with a drill.

I used an SB Tactical PDW brace. The slider bars hit the grip a little too soon so the brace cannot collapse all the way in.  However the buffer tube is installed anyway so even if the bars cleared the grip, the brace would only move about 1/2 and inch more before it hits the buffer tube.

The next modification was to add a Magpul Mossberg 500/590 handguard. This is not as easy as the Ergo Grip and SB Tactical Brace. The Magpul handguard does not work with the 590 Shockwave without a moderate amount of modification.

The problem is due to the action tube. The 590 Shockwave uses a shorter tube than a standard Mossberg 500. You can see the two below. So when you slide the Magpul handguard onto the 590 Shockwave tube, the threads are not long enough for the castle nut to grab onto it.

 

So you need to remove material from the handguard and expose the threads of the tube. I used a 1.5″ hole saw. It is a very tight fit and you have to force it into the handguard. One nice thing is that the handguard keeps the hole saw centered.You want to remove material down to the blue line in the photo below.

Oh and a tip from my machinst friend Keith, use liquid soap as a lubricant when machining plastic. Unfortunately he told me this nugget after I mauled up my handguard.

Next just use a pair of needle nose pliers and pry off the thin bits of plastic. Then use a sharp knife to debur the plastic.

It’s not pretty but it works.

Next up is to test fit it onto the action tube. There is a black anti-rotation ring that the castle nut indexes onto. I found it easier to remove material from the sides to make it fit rather than removing more material from the handguard.

Here is the final result.

How was shooting the Mossberg 590 Shockwave with a brace? Not as fun as my Vang Comp 870. The recoil was rather sharp. It was more pronounced that I am used to. Brian did not seem to mind but his 870 does not have any rubber padding and kicks horribly so this is nothing compared to that.

Conclusion

Now that I have shot the Shockwave like this, I think I will Form 1 it and make it into a SBS. I would prefer the Magpul stock on it and have Vang Comp tune the barrel a bit. Also threaded for Salvo 12 would be nice, like what Pete did with his Remington Tac-14. However I am now missing the compactness of the raptor bird’s head grip. It makes the whole gun feel smaller than it is. With the brace and pistol grip, the firearm loses its appeal a little bit.

While I am waiting on that, I will get a rail to mount an optic. We had to bury the bead in order to hit steel at 25 yards with slugs.

Considering the need to modify the Magpul handguard, I am ambivalent on whether the Remington Tac-14 is better than the Mossberg 590 Shockwave. As I pointed out, the Mossberg is drilled and tapped for a rail. The Remington is not. But the Remington comes with the Magpul hardguard. It would have been easier to have Keith drill and tap the Remington receiver for an optic rail.

The Mossberg 590 Shockwave is a fun little gun to shoot. However I don’t think this will be my go to gun for defense. If I am forced to use something that shoots shotshells then I rather grab my Keltec Shotgun for higher capacity. It is a lot more comfortable to shoot as well. Plus I don’t have problems with shells ejecting and hitting my wrists which is a problem for some people when shooting the KSG.