A History and Evolution of Mounts and Rails: Picatinny, KeyMod and M-LOK

A History and Evolution of Mounts and Rails: Picatinny, KeyMod and M-L

By firefield  

Until 2012, we only had two ways to mount accessories to our ARs and other Modern Sporting Rifles (MSRs)—Weaver and Picatinny. Both are based on the same principles of using rails and slots to mount optics and other accessories to firearms.

Though not the first, the Weaver mounting system was, and might still be, the most widely used. The Weaver mounting system was designed by William Ralph Weaver of Weaver Optics to mount the company’s scopes to rifles and incorporates flat dovetail rails with cross-wise slots. The slots are 0.180 inches wide, but the spacing on Weaver rails are not and have never been consistent. In the 1980s, the A.R.M.S. company started working on standardizing the Weaver rail system.  Then, Gary Houtsma, an engineer at Picatinny Arsenal—U.S. Military arms and ammo research, development and acquisition facility—took this new standardized rail for testing and evaluation and created the military standard for the Picatinny rail. The locking slot width on Picatinny rails is 0.206 inches, the spacing slot measures 0.394 inches and the slot depth is 0.118 inches. The U.S. Military adopted the Picatinny rail on February 3, 1995. Because of the inconsistency on Weaver rails, Weaver mounts will fit on Picatinny rails, but Picatinny mounts will not fit on Weaver rails.

Picatinny and Weaver rails require mounts for your mounts and add extra weight to your rifle. As the AR-15 gained popularity and technology advanced, people started experimenting with different materials to keep weight on their rifles down. Things like polymer lowers, and carbon fiber became accepted and even well-liked.


Firefield KeyMod handguard

One of these experimenters was Eric Kincel, who was at VLTOR Weapon Systems at the time. Kincel and VLTOR engineer Jeff O’Brien began building a handguard and rail system that would eliminate the 3, 6 and 9 o’clock position limitations, be lighter in weight with increased ventilation, not use loose screws and nuts easily lost and was also self-contained. According to Wikipedia, around the same time, Noveske Rifleworks founder John Noveske (1976-2013) approached Kincel with his own design of a direct attachment system. The two collaborated and decided to go with Kincel’s KeyMod (Modular Key Slot) system which uses a sleek key slot system typical of a shelving unit. The KeyMod handguard eliminates the infamous “cheese grater” design of the Picatinny handguard.

To mount a KeyMod accessory to a KeyMod handguard, you simply place the rail or accessory into the larger key slot, slide it to the smaller end and tighten it down with a screwdriver. In an interview with Ballistic Magazine in 2015, Kincel said, “One of the reasons that the American small arms industry has made so many advancements is standardized modularity, like the Picatinny rail. I wanted to make a standard that all the industry designers and engineers were free to use, build products for and move the industry forward, like the MIL-STD-1913 Picatinny rail, which everyone could utilize. Also, by having the industry working together, the new standard would offer a wider accessory range, which is so much better for the end user.”

KeyMod Advantages:

  • Solid lock-up
  • Self-aligning
  • Repeats zero
  • Recoil proof

KeyMod accessories are easy and quick to mount and offer a solid lock-up. One disadvantage of the KeyMod system is that accessories will only mount in one direction on the rear of the slot. Kincel decided to keep KeyMod open source so anyone can download the specs and make their own KeyMod handguard and accessories. The specs have been public since July 2012.


Magpul MOE M-LOK handguard

There was a slight problem with KeyMod, though. The KeyMod handguard didn’t do well with plastic accessories… i.e.: Magpul. Magpul Industries, inventors of the PMAG, is one of the most popular brands of AR-15 accessories (I myself am a big fan.) In 2014, Magpul released the Modular Lock (M-LOK) MOE handguard. M-LOK uses T nuts and screws to clamp down accessories. M-LOK has specific measurements you must follow if you are going to make one. Magpul won’t align itself with any product that does not follow its core values, so it does not open source M-LOK. The license is free; however, you must ask Magpul for permission and specs to manufacturer M-LOK.

Both M-LOK and KeyMod help reduce weight and have accessories that directly attach to the handguard without needing to use extra rails.

M-LOK Advantages:

  • Cheaper to manufacture
  • Works with plastic handguards
  • Attach accessories to the front or rear
  • Passed USSCOM stress test

One benefit M-LOK has over KeyMod is that USSOCOM chose M-LOK over KeyMod. M-LOK performed better during rigorous drop testing, which some find the be-all and end-all of endorsements, but those of us who aren’t MIL-SPEC snobs will weigh our options fairly. I mean, unless you are an operator, you won’t be running your gun like our Special Forces and either M-LOK or KeyMod will be good for your uses.

As far as which one is better is totally up to you… Like most typical arguments in the gun community, the KeyMod versus M-LOK debate will rage forever without a correct answer.

KeyMod, M-LOK or Picatinny? Tell us which one you prefer and why in the comment section.

(Side note: In case you were wondering…I run Picatinny on both my AR-15s.)

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