Anyone who ever watched what’s easily the best action movie ever, The Predator, wanted a bottom-mounted shotgun. As a kid, Billy was always my favorite character, and his M16-wannabe with the attached Mossberg 500 captured me. As I grew up and got into guns, systems like the KAC Masterkey fascinated me.
The idea evolved and expanded. The U.S. Army liked the idea enough to adopt the M26 MAS. This straight-pull bolt-action, box mag-fed shotgun attached to the bottom of an M4. How many were adopted is beyond me. How many were fielded is also beyond me. I’d bet it is an absurdly rare configuration in Army use.
Advertisement — Continue Reading Below
Shotguns are already super rare in military use, so a bottom-mounted shotgun attached to an M4 must be absurdly rare. There is a reason, as I’ve finally made my own dream come true. Kind of.
Where it Starts
A couple of years ago, a local dealer had a parts kit for a Mossberg Compact Cruiser 590A1. This is a 10.25-inch barrel, three-round magazine tube, and vertical foregrip pump. I purchased it, filed a Form 1, and made a short-barreled shotgun. This is an absurdly small short-barreled shotgun, and it turns out that it’s the right size to mount to a standard AR-15 carbine.
There are kits and attachment systems to bottom-mount shotguns. They can be tough to find and are pricey. My excuse is that I wanted to try the entire setup as a concept before I tried to find one of these kits and spend the hard-earned money on it.
Advertisement — Continue Reading Below
That’s the logical excuse; the other excuse is that I’m impatient, so I sought out an easier way to do it. Mossbergs are drilled and tapped for an optic rail. I added an optic’s rail to the gun, and then purchased two Picatinny rail-to-rail adapters.
This is not optimum. In fact, it’s terrible. Don’t do this. Eventually the tiny screws holding the optic rail to the gun will snap, forcing me to drill them out. Still, I had a bottom-mounted shotgun on my AR-15.
Advertisement — Continue Reading Below
Bottom Mounted Shotguns Are Awful
This is a bit of a duh moment, right? I mean, if it actually worked well, more people would use it. As the name implies, the KAC Masterkey was designed to attach a breaching shotgun to a rifle to streamline things. We saw a little use of these guns by some of the fancy special operators, but they never really took off.
It’s easy to see why. Attaching a shotgun to a rifle makes for a terrible experience with both. Admittedly, if this was your setup, you’d be breaching doors with the shotgun, not using it for CQB. Breaching a door with a shotgun doesn’t require an incredibly ergonomic experience.
Advertisement — Continue Reading Below
Predictably, the weight of the shotgun creates an incredibly unbalanced weapon. There isn’t much of a space to put your hand, and reaching to the vertical grip on the bottom-mounted shotgun is a bit of a stretch. Thankfully, AR recoil isn’t all that bad, so you can make hits.
I fired mini-shell birdshot from the shotgun. I wanted as little recoil as possible to try and avoid snapping the optic rail screws. This worked fine for my purpose. Aiming the shotgun is an experience. You have to chicken-wing the stock under your shoulder to actually pump the gun.
It’d be tough to handle higher recoiling rounds out of a shotgun with this setup. Not that it would beat you up, but try to do any kind of recoil mitigation for fast follow-ups. In a breaching role, it’s fine.
Advertisement — Continue Reading Below
The few breaching rounds I’ve fired don’t have much recoil anyway. The same goes for the mini-shell birdshot. It’s fine, but still not easy to shoot with any kind of speed. I can see why the M26 MASS uses a side-mounted, straight-pull action.
It’s Still Rad
Something doesn’t have to work well to appreciate it, right? The setup still looks fun, but it’s easy to see why everyone preferred a separate breaching shotgun like the Remington MCS system. Even grenade launchers went from the M203 to the more portable handheld M320 series.
Advertisement — Continue Reading Below
It turns out that attaching a gun to your gun isn’t as fun as Xzibit told us it would be.
Read the full article here
