The KeyMod Versus M-LOK Debate

BY Herschel Smith
1 year, 5 months ago

Daniel Defense.

If you’ve done any online research on which type of rail to get for your AR, you’ve probably come across more than one article, forum, or video proclaiming that KeyMod rails are dying or, in the opinion of some, already dead. But is it true?

First off, let’s be clear about one thing—there are plenty of firearms out there equipped with KeyMod rails, including the Daniel Defense DDM4ISR, so the rail system is not being called dying or dead by some because you can no longer find or buy it. There are also still plenty of accessories from many different manufacturers available for KeyMod rails. So, those using terms like “dying” or “dead” are referring to KeyMod’s status compared to that of its main competitor, the M-LOK rail. But KeyMod, M-LOK, and Picatinny rails are all viable options for an AR rail. Which is why all three types are manufactured and sold by Daniel Defense.

The Origin of KeyMod’s So-Called Death

KeyMod was developed by VLTOR and released in 2012, so it had roughly three years to gain some traction before MAGPUL released its M-LOK system in 2015.

I’ve said before that KeyMod was designed by Noveske and M-LOK by Magpul.  As noted above, this isn’t quite the case.  KeyMod was designed by VLTOR and released through Noveske, soon becoming open source.

Unlike a Picatinny rail, which is a “positive” or “male” system and can be bulky, sharp, and tough on the hands, both KeyMod and M-LOK rails are lower-profile “negative” or “female” systems. For those of you not familiar with either system, here’s a brief description of how they work:

  • KeyMod works by inserting an accessory’s mounting nuts through the large holes of key-shaped slots (which resemble slots in industrial shelving) in the handguard. You then slide the accessory forward, into the smaller front portion of the slot, and tighten the mounting bolts.
  • M-LOK works by inserting the “T-nuts” of an accessory through slots in the handguard and then tightening the bolts on the accessory. This rotates the T-nuts 90 degrees and locks the accessory in place.

As you might imagine, as with any new gun accessory, as the systems were introduced, there were fans of both, and many weren’t shy about pronouncing their choice superior to all others. For a couple of years, these two systems went mano e mano as a lighter-weight, lower-profile option to a Picatinny rail as the debate raged on.

But then, in 2016, the Naval Surface Warfare Center, Crane Division, conducted testing that compared KeyMod and M-LOK head-to-head. You can view the details of the test and the results here, but suffice it to say that M-LOK fared better than KeyMod in testing categories that included repeatability, endurance, rough handling, a drop test, and failure load.

After Crane’s test results were presented in May of 2017, many considered the debate over and pronounced M-LOK the superior choice. But does one study really spell the death of an entire rail system? Daniel Defense obviously thinks not, for the following reasons:

1. Most AR Owners Are Not Members of the Special Ops Community

The study conducted by Crane was at the behest of USSOCOM, to determine which rail system might best meet their needs. But, if you’re a recreational shooter, chances are you’re not going to put the rail on your rifle through the same level of use and abuse as elite military professionals. While it’s true that many consumers want to use the same gear as military and law enforcement pros, for the vast majority of shooters, a KeyMod rail is going to perform flawlessly.

2. KeyMod Accessories Don’t Protrude as far into the Rail as M-LOK Accessories

The bolts that tighten the mounting nuts of a KeyMod accessory do not protrude through the rail as physically far as the bolts that tighten the T-nuts of an M-LOK accessory, so a KeyMod rail can fit snugger and be closer to the barrel of a firearm.

This may not sound like much of an issue, but on firearms with very little clearance between the barrel and the rail, it can be—especially if the bolt of an M-LOK T-nut were to protrude far enough to actually touch the barrel and affect its harmonics. Which is precisely why a KeyMod MFR XL 15” rail is used on the DDM4ISR, which features a suppressor as an integral part of the barrel.

“The way M-LOK fasteners on accessories attach to the handguard, they would interfere with the suppressor tube underneath the handguards,” explains Daniel Defense Law Enforcement Sales Manager Joe Marler. “You cannot mount an M-LOK accessory where that suppressor tube is present. KeyMod accessories have very low-profile fasteners, and that’s the reason we use a KeyMod rail.”

Mr. GunsnGear explains the same thing in his YouTube review of the DDM4ISR at about the 11:30 mark of this 24-minute review. He also backs up our #1 point with his review when he states, “For 99.9% of the people out there, KeyMod is going to be just fine. KeyMod has been used by special operations units around the world, and nobody died because of KeyMod.”

I didn’t even look up the purported 2016 report and don’t care what’s in it.  Nor do I think this has anything to do with whether you intend on trying out for JSOC.  You can find a report to tell you anything you want to hear.

The whole debate is childish in my opinion, or a different way of saying it is that while I think the DD article is informative and good, to say that one approach is “dead” reeks of marketing lies to me.

I think it comes down to what you want to use.  For me, I’ve seen the T-nuts on M-LOK wiggle loose and parts fall off, and that’s after aggressive tightening.  I think they’re harder to install, and finally, KeyMod is lighter by design.

KeyMod works with less forend metal (with its cutouts) without creating a stress concentration point from sharp edges.

I prefer KeyMod.  Others prefer M-LOK.  Buy what you want, but don’t get swept into hours of reading to determine what “experts” prefer.  Figure out what’s best for you.


  1. On February 21, 2021 at 10:09 pm, Georgiaboy61 said:

    @ Herschel

    Read you five-by-five concerning preferences for/against Key-Mod, M-LOK, or any other mounting system. Use what works for you, and chances are you’ll be OK. It should also be said that plenty of tier one types still use the now well-established M1913 Picatinny Stanag mounting system with Knights Armament rail covers on unused portions of the rail.

  2. On February 22, 2021 at 8:44 am, Furminator said:

    Comes down to availability in my neck of the woods. Anything you need for M-Lok at multiple stores, one 3-inch keymod rail section at one store. Had to order a keymod QD connector from Midway to finish the only gun I built with that system.

  3. On February 22, 2021 at 9:45 am, Ron said:

    “… You can find a report to tell you anything you want to hear. …”


    Statistics lie and liars use statistics.

    Make up your own mind and don’t worry about who says you’re wrong.
    If you have good reasons,
    That’s good enough.

    I use M-Lok too, because it was out earlier and it still fullfills my needs.
    And it’s K.I.S.S. in action

  4. On February 22, 2021 at 9:51 am, Ron said:

    And as proof how much difference it really makes, I got it bass-ackwards!!


    I use KeyMod.

    Just checked.

    And after all, once the add-ons are installed and it works for you, are you going to be removing and reinstalling often?

    Probably not

  5. On February 22, 2021 at 10:39 am, George 1 said:

    Key-Mod is less readily available in my neck of the woods. In my experience Herschel is right though. Key-Mod is easier to install or change out parts in the field. Key-mod has worked fine for me on the one weapon I have with it. Never had any problems with anything coming loose and it is my beater rifle.

    I have a flashlight, a vertical forward grip and a QD sling attachment on the rifle all using Key-mod attachment points. The rifle has been well used and is the one I have always used the most in firearms classes and other training. My son has used it a bunch of times as well. Never had a problem with the Key-mod.

  6. On February 22, 2021 at 5:03 pm, VietVet said:

    Either system is acceptable to me, I’ve got rifles with both and they have always done the intended job. That said I don’t load my rifles up with gadgets that I don’t need.

    I do have one rifle that I built myself, designed for SPR use with a 20” JP Engineering stainless wylde chambering and a heavy barrel profile. The forend is JP Engineering small diameter tube and Keymod is the proper configuration because the M-lock tube I originally installed caused the screws to impact the barrel.

    M-lock is more readily available around here but I mail order most things I need anyway. I’ve never had a failure of either but I also use locktite for attaching screws so that they don’t back out.

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You are currently reading "The KeyMod Versus M-LOK Debate", entry #26960 on The Captain's Journal.

This article is filed under the category(s) AR-15s and was published February 21st, 2021 by Herschel Smith.

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