Defender Tactical CoSight for Mossberg Shotguns

I don’t work for Defender Tactical, and I have never received any compensation from Defender Tactical. However, I did have a hand in designing their new CoSight system you see here. I don’t want to overstate how much work I did. If we broke it down, it was probably about two percent while the father and son team at Defender Tactical did 98%.

My work on the CoSight amounted to emailing them and describing what I think would be an awesome sight/red dot mount. Following that, I kept asking annoying questions and inquiring about different configurations of the CoSight.

I don’t receive any compensation for the sales or success of the CoSight, but Defender Tactical did send me two for free. With all of that out of the way, I’m proud of the two percent of the work I did, and the CoSight is what I’ve wanted from shotgun sights for a long time.

The Idea Behind the CoSight

I really like rifle sights on shotguns. Think Ithaca Deer Slayer-style sights that sit on the barrel. To me, they’re the perfect balance of speed and precision. These are more or less Safari-style sights that are used for shooting big, dangerous game at close ranges. Sadly, no one really makes those for shotguns anymore.

Sights like these.

I looked and looked, and custom shops can do it for quite a bit of money. But these sights don’t work well with modern red dots, which tend to be the fastest and most precise option on shotguns.

My goal was open iron sights designed to be quick and mated to a red dot mount that keeps the red dot low tp enable cowitnessing. The finished CoSight mount uses the Trijicon RMR footprint for optics.

The GLOCK sights were a natural choice due to how easy it is to find them. (Travis Pike for TTAG)

I understand people like options, and they understandably like things to be affordable. That’s why GLOCK sights were chosen as the open sights. They’re common and can be as cheap or as expensive as you want them to be. They come in suppressor-height variations, night sights, big dots, and even ghost ring rear sights. If you really loved ghost rings on shotguns, then you still have that option.

My CoSight Setup

I like ghost rings, but for shotgun work, I find open sights are faster and plenty precise. Open sights are better than a bead sight and give me enough precision for slugs and the speed needed for buckshot.

The CoSight allows you to place a front and rear GLOCK sight on your gun if you’re dealing with just a bead. Yes, it’s a short sight radius, but it’s built for speed. My CoSight is set up to use a suppressor-height GLOCK rear sight along with my Mossberg 590 front rifle sight.

The Ameriglo rear sight is all I need, but the mount accommodates a GLOCK front sight. (Travis Pike for TTAG)

The front slot is empty, and I have a long sight radius and an iron sight that provided a lower third cowitness through my Holosun 509T. It’s a fantastic combination. I have my iron sight option and my red dot option. This makes for a lot of versatility. I can zero the optic for slugs and use the irons for buckshot if I so chose. For home defense, it’s a buckshot-only gun, but it works really well.


You’ll need some way to tap your GLOCK rear sight into the groove. A sight pusher works best (XS makes some great options). You’ll also need a front sight tool to attach the front GLOCK sight if you use one.

Installing the GLOCK sights is the hardest part of the operation, but it’s very straightforward. Sometimes you feel like you need three hands with a sight pusher, but that’s pretty much a universal feeling with sight pushers. You can also order the CoSight with a sight pre-installed for a few dollars more. If you don’t own a sight pusher, that’s the more affordable option.

Installation is really simple. (Travis Pike for TTAG)

Installing the CoSight on your shotgun is easy enough. Mossberg 500 series guns are drilled and tapped from the factory. I had to remove my ghost ring sights. Let me tell you, that was the hardest part. However, the CoSight installs and screws on with very little difficulty. You then install your red dot optic of choice and you’re off to the races.

At the Range

I left the optic off for the first part of my testing, using only the open sights. The rear sight is a .394-inch tall sight from Ameriglo. It works perfectly sighting through the 509T and lines up with the front sight of the Mossberg 590A1. With a different optic, you’d get an absolute cowitness, but the 509 T’s enclosed emitter design and plate system make it sit a bit higher.

See that Cowitness? (Travis Pike for TTAG)

I use Federal Flitecontrol for home defense, and that isn’t a load that spreads much at home defense ranges. I like having a little more precision to take advantage of the tight patterning design of the Flitecontrol load. Having a front and rear sight allows that. With that said, I could always just use the front sight for speed, much like a bead sight.

I spent a little time and shot some Flitecontrol, practicing both speed and accuracy drills. The sights line up perfectly when I mount the gun, and it’s not something I have to spend time perfecting or adjusting to. I was capable of quick and accurate shots with just the irons. I shot at 15 and 25 yards with the Flitecontrol loads and went back to 50 yards with the slugs and rang steel over and over.

The sighting solution is precise and fast. (Travis Pike for TTAG)

I dialed in the Holosun 509T and after zeroing the optic, I was even faster. I prefer the Holosun because of its 32 MOA circle. I pattern my Flitecontrol load inside that circle, and I know it stays there within 15 yards. The CoSight mount held the optic tight, and zeroing wasn’t a problem.

My Solution

The CoSight is just what I wanted in a shotgun sight. I shoot shotguns a lot and I’ve tried and experimented with a number of sighting solutions. I might be biased, but the CoSight offers exactly what I want from a sighting system, combining red dot compatibility and open sights. With that said, it’s also modular, and you can add whatever style GLOCK sight you choose.

A red dot is a natural pairing for the shotgun. (Travis Pike for TTAG)

The CoSight allows you to get the most out of rifle-style front sights and move beyond the bead without having to contact a gunsmith. While I haven’t tried it just yet, I’m willing to bet it pairs well with the Defender Tactical HighBall front sight, too.

They’re on sale now for $70 for the mount and $99 for the mount with iron sights preinstalled. Again, I don’t receive any compensation if you purchase one, but I’m proud of it.

Check it out here. 


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