The only thing we love more than buying and shooting new guns is buying cool stuff to put on them, but to do that you need a solid mounting platform.
In the world of the AR-15 that comes down to three major options -- Picatinny 1913 railing, M-LOK, and KeyMod.
And really if you’re looking at a modern rifle, it’s down to KeyMod or M-LOK.
But what is the difference? What does it all mean? Stick around and find out!
M-LOK, KeyMod, Picatinny 1913, and Weaver Railings
To really understand M-LOK and KeyMod we need to talk about Dovetail, Weaver, and Picatinny 1913 railing first.
While most of these started out as ways to mount optics to rifles, the attachment systems have grown past that and now extend to weapon lights and lasers, grips, bipods, and other attachments.
Back in the old, old days Dovetail mounts were very common in sporting rifles. These are basically two pieces of metal that are cut in a fashion to allow one to slide tightly over or into the other.
Dovetail is very easy to make, easy to use, and holds well enough to get your yearly deer. But since it relies almost entirely on clamping force, it really isn’t very strong. Even still, you can find it on some rimfire and many air guns to this day.
Weaver and Picatinny
Weaver railing externally is similar to dovetail but has the added benefit of cross cuts so a bar or screw can be placed through the material. This provides a stronger clamping force but also a physical object to lock the attachment in place.
Picatinny or MIL-STD-1913 visually look very much like Weaver and fundamentally they work the same way, however, they are radically different specifications.
While Weaver is more rounded and Picatinny is sharper and more square, the major difference mechanically is that the gaps between ridges in Picatinny are a standardized size. Weaver is looser and questionable.
Most Weaver attachments will fit on Picatinny, but most Picatinny won’t fit on Weaver.
Keymod was the first big step forward in attachment design in almost 20 years. While Picatinny had been around since 1995, in 2012 KeyMod burst onto the scene as an open-source method of attachment designed by VLTOR Weapon Systems and Noveske Rifleworks.
Sounding very much like the name, the system uses two parts with the mounting surface having keyhole cuts and the attachment having metal pegs that are rounded and protruding to one side.
Simply insert the pegs with the protrusion facing forward into the keyholes and then turn the pegs with a driver bit to tighten and lock.
M-LOK was designed by Magpul after seeing that KeyMod didn’t work to their liking with their polymer parts. Relaced in 2014 as a free license product M-LOK works on the same idea as KeyMod in that there is a male and female part that lock together.
M-LOK’s slots are long rectangles and the pegs are cut with more of a T shape. Simple turn the T shape pegs so they fit in the slot, press down, and using a driver turn the pegs so the T’s lock down and clamp the attachment to the surface.
Why Replace Picatinny 1913 Railing?
You might be wondering why did Picatinny need to be replaced? I mean, we still use it for optics -- so it can’t be that bad, right?
Well, yes and no.
Picatinny 1913 railing is a great way of attaching things and is perfect for optics on top of weapons or lights on the bottom of pistols where space is limited.
However, when you try to expand the system so you can mount whatever you want wherever you want -- such as with a full handguard, Picatinny has two major problems.
First, it’s heavy. A 15” Picatinny quad-rail is about 17 ounces, and an M-LOK rail of the same length is around 11.5 ounces. A full third of a pound lighter on the front end of your rifle makes a big difference.
Secondly, holding a quad-rail kind of really sucks. These rails quickly got the name “cheese grater rails” because it kind of feels like holding one. Do any running or movement while holding on and it can start to cut your hand if you’re not careful.
Seeing both of these as an issue worth solving, the United States Special Operations Command (USSOCOM) around 2015 wanted to look around and see if one of the newer options were worth considering.
M-LOK Vs. KeyMod
That testing came down to two options: M-LOK or KeyMod.
Both were tested and found that both were very nice to handle, no more grated cheese hands.
Both are economical to make/buy, both have a wide range of attachments, and both do their jobs well.
However, M-LOK proved to be better. A lot better.
The full testing report isn’t available but a summary of the report is.
Bottom line, M-LOK won because of drop tests, repeatability, and max load.
KeyMod and M-LOK were found to work very well under normal conditions, like shooting a rifle. But it was the extras that pushed M-LOK forward.
In drop testing it was found that KeyMod only held on to 33% of its attachments, M-LOK held onto 100% in the same testing.
When removing and reinstalling sighting systems like lasers, M-LOK had a standard point-of-aim (POA) variance of about 1.3 MOA -- this was 1/4th the amount as “some other systems” (read, KeyMod) showed. While you should always re-zero your sighting systems, closer is better.
And finally, for max load M-LOK outperformed “some other systems” by more than 3-times the amount of weight and it even outperformed Picatinny 1913 railing.
When it comes down to it -- M-LOK is objectively better than KeyMod.
What Is Best For You?
The short answer is M-LOK.
Not only did M-LOK simply test better than KeyMod did, that testing also kind of killed KeyMod as an option. In fact, I can’t even remember the last time I saw anyone offering a KeyMod rail or rifle that wasn’t a part of a super-ultra-warehouse-old-stock-clearence sale.
Once USSOCOM says something is the best the market quickly follows.
That being said, if you already have KeyMod and are happy with it -- there isn’t a major reason to switch. USSOCOM testing is extreme for good reason and you the normal user are never likely to heap that much abuse onto your rifle, so KeyMod is a safe option.
But if you’re building or buying a new handguard or rifle, I would strongly recommend ignoring even the best sale on KeyMod and picking M-LOK instead.
Finding accessories in KeyMod is harder than finding a rail to mount it on.
But if you want that classic GWOT look, Picatinny 1913 railing is still a solid option. Just bring gloves or rail covers.
Like Betamax Vs. VHS, KeyMod Vs. M-LOK had one clear winner and the rest is history. Easy to use, easy to swap around, M-LOK is a great mounting platform for anything from foregrips to flashlights to lasers.
[We would like to extend a huge thank you to David Lane for his hard work on this article! Drop a comment below with your perspective and make sure to check out our other articles such as AR-15 Calibers and 300 Blackout vs. 7.62x39.]