• Mossberg Owners is in the process of upgrading the software. Please bear with us while we transition to the new look and new upgraded software.

New 590S


Seems Mossberg has developed a a new shockwave that will feed different length shells without an adapter.

Does anyone know how this works and can mine be retrofit to do this?
I have not seen one and I'm not sure a parts schematic for the 590S has been released yet. But here's a write up that explains the three major changes.

If it ain’t broke, don’t fix it. Mossberg appears to have agreed with this principle of design while reworking the 590, as most of its well-proven design remained the same in the new Mossberg 590S. The only “problem” worth addressing was the design’s inability to reliably feed mini shells—something that virtually no pump-action or automatic shotgun has been able to do consistently. To remedy this, all that needed changing on the 590S were its elevator and bolt slide. An energy-absorbing buffer was also added. The end result is a shotgun that feeds 2.75 and 3-inch shells just as reliably as before, but now with the ability to add 1.75-inch shells to the mix. Mossberg claims that the 590S will run reliably with a mix of ammo in any order, and varying load types or shell lengths will not cause problems. If it’s a 12-gauge round it can be stuffed in the tube, pumped into the chamber and fired without issue.

Hopefully someone can do a side by side breakdown of the two models to show the design differences with photos.

I think aguila is about the only company making the short shells. Off the top of my head, I can't think of anyone else that does. Though, I'm sure reloaders could cut a shell down to length and roll crimp them.

But, all that aside, I'm glad that mossberg was able to figure out how to do it for those that do want to use the short shells and increase their capacity. If it's as simple as replacing a part or two, for anyone inclined to do it, doesn't sound very hard to do. The mossberg is one of easiest pumps to take apart. I have a few pumps that I hate taking apart much worse than the mossy.
After doing a little more research last night it appears the bolt carrier is machine to account for the longer tongue on the lifter. And there is a hard bumper to the back to soften the magazine shoot out of the 1.75" shells since they are lighter to keep them from bouncing up.

Hopefully someone who owns a 590S will tear it down and take some pictures.

In time, mossberg may sell "conversion parts" or eventually, the parts will end up on ebay and numrich gun parts and other places just like they do now.
Defender Tactical makes an adapter that will feed any length shell, even a mixture of different length shells.

Mine arrived and installation commenced.

For some reason the trigger group refused to go back in, but nothing to do it with the adapter. Something was catching and it was spongy and not dropping into the receiver. Of course, there's nothing on the internet to help you fix it. Everything inside the receiver was were it's supposed to be, the bolt was fully forward. I still don't know what it was, but after 68 tries it dropped in place just fine.

It cycles the mini shells perfectly. It acts as a bumper to prevent them from flipping over. I was able to load 8 +1 which is really nice for such a compact not-a-shotgun. It cycled minis mixed with others without a hiccup.

This has opened this gun up to be a great home protection arm. Cheaper and much easier than dealing with, and waiting for, Mossberg.
Last edited:
I really like the idea of being able to mix and match shell lengths. I thought about upgrading to the Shockwave 590s, but I'd probably lose quite a bit of money in the deal. Now I've got one of the adapter kits in the mail. It seems simple enough to install, so I'll give it a shot. Thanks for the heads-up.
Is it absolutely necessary to replace the follower? Not sure if I see the point of doing so.
I didn’t at first but 2 loaded mags in a row stood up the last shell, which was a mini both times. Since the new follower only took a minute or less to install and it’s more pointy? shape seems to maybe push that last mini back a hair farther into the adapter. No problems after in any case.
Defender tactical is now a forum sponsor. If you have a review or post about them, I'm sure everyone would love to learn more about it.

I'm curious what is necessary and how it's installed and retained in the receiver, etc.

Here ya go:

Here's our installation video for the whole kit! The majority covers the follower install as we had to address 500 and 590, but the adapter install starts at 5:30 and only takes about 60 seconds. Let me know if you have any other questions!

Question for those of you that have installed this upgrade and have fired some shells thru it. Does it pinch your thumb when reloading at all?
I’ve not fired any rounds through the gun with this little adapter installed. Just stuffed the shells in and cycled them out by jacking the slide. The adapter is semi flexible and made of some kind of plastic. It only acts on the loading aspect, so whether you fire the round or not shouldn’t be any different. My thumb barely pushes the adapter up to load a shell and I’ve not pinched anything putting a shell in the mag.( ever). Dropping the initial round into the gun through the ejection port could be dicey for some, but I’ve not had any issues and this little piece certainly doesn’t add any..good luck
Question for those of you that have installed this upgrade and have fired some shells thru it. Does it pinch your thumb when reloading at all?
No, you don't even notice that it's installed while loading. The only time you might need to do something different is if you unload your mag by pressing the cartridge stop, you may need to depress the tongue on the adapter to move it out of the way so the shell can eject. Other than that, completely transparent to the function of the weapon.