As a big shotgun nerd, it can get frustrating to mount optics to different guns. With handguns and ARs, we have a fairly typical optics footprint. Handguns have a few different direct-mount optics, and ARs all have a flattop upper these days. Shotguns, on the other hand, all use different mounting patterns that leave you searching for mounts and rails to fit. Monstrum Tactical has decided that’s not good enough and released a series of Grimlock mounts.
Mounting Optics with Monstrum Tactical Grimlock Mounts
If you’ve ever used the new Vortex Viper shotgun dot, you have a good idea of how these mounts work. They have three slots. One is a single screw hole that’s simple and acts as your base. You align this hole with the rearmost screw on your shotgun and attach it.
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Just forward of the base hole is a short slot that allows you to mount the second screw. This longer, elongated slot allows you to put the second screw wherever it needs to be. Forward of that slot is another, even longer, elongated slot. Here you can mount your third or even fourth screw to finish mounting the optic. It’s such a simple idea that I kick myself for not thinking of it.
Configurations and Compatibility
The Grimlock comes in three universal configurations. We have two direct-footprint mounts to work with RMR and RMSc optics. The third is a plain Picatinny mount for mounting any optic. I purchased both the Picatinny mount and the direct RMSc mount. There is also a Grimlock mount made exclusively for the Mossberg series of shotguns.
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The Grimlock mounts come with #8-40 and #6-48 gunsmithing screws and will fit basically all Mossbergs that are optics-ready, optics-ready 870s, the Benelli M1, M2, M3, M4, and, in my testing, it works with the Nova as well. It also fits the Winchester 1300 and the Stoeger M3000/M3500 series.
However, if you only look at shotguns, you lack creativity. I was able to mount the Grimlock to the Henry Homesteader, which shows it works with Henry rail footprints. I also mounted the direct-mount RMSc option to my Rossi Brawler in .300 Blackout without a problem.
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Mounted Up with the Grimlock
I’m a shotgun guy using shotgun mounts on guns that aren’t shotguns. It seems silly, but I wanted to test the flexibility of the optics mounts, and I’m pleasantly surprised by their flexibility. Since they cost right around $20 each, I’ll probably pick up more and start outfitting my optics-ready shotguns with optics.
Equipping the Homesteader requires you to use the right screws. The Grimlock series comes with plenty, but my initial mounting put the screws too deep into the receiver and caught the bolt. I swapped them immediately and never tried to fire the gun with the bolt dragging against the screws.
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Whenever you use these mounts, do a function check. If it doesn’t feel smooth, then it’s not good to go. Luckily, that’s not a tough fix since the Grimlock mounts come with so many screws.
Range Testing: 9mm and .300 Blackout
At the range, I figured the 9mm Henry Homesteader wouldn’t be too much for the mount to handle. I did think the recoil of a rifle round through a short pistol might be a challenge with the Brawler. With the mounts mounted, I hit the range with a healthy dose of 9mm and .300 Blackout and let it fly.
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The mounts held steady, aided by a dab of Loctite to the attachment screws. I zeroed my old Bushnell TRS-25 and Swampfox Sentinel 2 and shot a healthy amount of 9mm and 80 .300 Blackout rounds. Eighty isn’t a ton, but a box of .300 Blackout costs more than the optic mount.
The mounts held strong. At the end of the session, they remained in place, locked down and unmoving. Not bad for a $20 mount.
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Final Thoughts on Universal Mounts
The Grimlock mounts are a grand idea. They offer a high degree of usability at a great price. While they’re intended for shotguns, they work for a wide variety of firearms. The Grimlock mounts can be extremely useful if you want a low-mount design on weapons with unique optic mount footprints. For 20 bucks, I’m going to keep a few in the optics box for use in the future with review shotguns.
