What is the difference between Picatinny and M-LOK?

Attachment systems on firearms are a vital part of any firearm, not just the AR platform. The receiver of a rifle has an attachment system, an M249 handguard is now an attachment system, the bottom of a pistol frame is an attachment system. They all serve the same purpose though, allowing the user to put something on the gun that hopefully..doesn’t move or fall off. In this article, we will look at the origins and differences of Picatinny vs. M-LOK.

The uses of Picatinny has went from the AR platform to our machine guns as well. Notice the front rail on this M249. Soldiers now use it to mount PEQ-15’s and other accessories. Photo: FNAmerica

So where does that put us? Well, it puts us in decades of dispute as to “what attachment system is better”. Not only us, but the military joined the fight as well. These two very trustworthy attachment systems have allowed both civilians and the military to attach optics, lasers, and lights onto their firearms without them moving. We will also go over the importance of knowing your specific attachment system and lay out some Gunsmith tips and tricks to mount your accessories on these systems properly.

Don’t worry, after you read this article, you too can enter yet another firearm debate. Yay!

Rail systems have definitely come a long way and I don’t foresee changes stopping any time soon. Whether it is an older system such as Picatinny or a newer rail system such as M-LOK both are very important to the technological advances we have within our firearms.

Origins and Current History

As far as what came first, the Picatinny mounting system, later standardized by the Military as MIL-STD1913, came much, much before the Modular Lock (M-LOK) system from Magpul. However, both are still being used heavily today. The Picatinny mount, named after Picatinny Arsenal, has become an open source and Magpul’s M-LOK has allowed for a license to be obtained from Magpul if any other companies want to use it. Freedom in design allows for vast improvements and advances in firearm engineering, so thank you for that.

Picatinny

Now for chicken and the hen..what came first: C. Reed Knight Jr.’s invention of the Knights Armament Quad Rail or Picatinny from Picatinny Arsenal? The story of how the Knights Armament Rail Integrated System (RIS) influenced the Government to invent Picatinny is here, and it is quite entertaining and eye opening. You decide for yourself. Focus on the part where Mr.Knight allowed military folk to go from taping a flashlight onto their gun with duct tape, to giving us a quad rail and modular methods to attach foregrips and lights.

Anyway..no matter what came first, the very heavily used Rail Adapter System (RAS) from Knights Armament now has the Picatinny interface.

That Picatinny interface being given to us officially by Picatinny Arsenal and engineered by Gary Houtsma. More information on that here.

M-LOK

The origins of M-LOK go back to 2007 with the Masada Concept Rifle. This rifle, designed by Magpul, featured three slots in the front that allowed for the mounting of an accessory. This then leads to Magpul’s MOE line, which is still a very popular line of lightweight handguards. However, the M-LOK design wasn’t quite there due to needing to take the handguard off to mount anything to it. Yikes. Now, we have M-LOK, standing for Modular Lock. The rail slot shapes were adjusted and squared off and the mounting hardware was also changed a bit. More information on the history, specs, and how to install can be found here in a Magpul Press Release on M-LOK uploaded online by Giessele.

M-LOK is now being produced by almost every large firearm manufacturer and is being adopted by various military and Federal entities.

You will see in our best AR-15 handguards article we suggest both M-LOK and picatinny options.

Picatinny on top, MLOK on bottom

Designs and Pro’s/Con’s

The design for the two systems are very different. You will often be able to tell right away when looking at a hand rail or an accessory that mounts to a rail which system that product is designed for.

Picatinny

The picatinny mounting system is a slotted and clamping type of system. The rail has individual slots often marked with numbers. That way, you can remember where your accessory was mounted if you need to take it off and remount it. Your accessory will have a bar on the mounting plate that fits into those slots. On the side of the mounting plate, there will also be a locking/clamping type of bar. Place your accessory in your chosen slot and tighten down the locking screw, which then tightens the clamping bars to the side of the rail. Therefore, not only is there a bar accepting recoil but also clamps on the side of the rail.

• Common – Picatinny is still everywhere, even though it is forty years old. Look at a receiver of any AR platform or the newest hand rail of a M249, picatinny. Look at a lot of lasers and lights that are meant to mount on the side of a rifle. They will often have a picatinny plate already on the laser.
• Quick Detach Options – Picatinny is prevalent in allowing quick detach accessories, such as accessories with a tensioning lever, to make it easy to take on and off of accessories.
• Versatile – Now Picatinny is even being used in the archery world, to mount sights to bows.
• Simple – It is super simple to use. Simply fit the mount into a slot and tighten.
• Strength – The system is also strong. Get a dent or hit to the rail and your accessories should still hold. Why else would they would still use it as the main system for mounting an optic? Something that needs to hold zero always.

• Nock Offs – It is also everywhere, which means that some company may not be following proper MIL-STD1913 specifications. The more slop in those specifications means more movement to your accessory in the middle of those slots.
• Height – It also pushes your optics even higher and more outwards due to needing that rail space that the sides of the rail clamps onto.
• Bulky – it is pretty bulky. Wrapping small hands around a quad rail with picatinny on each side of the rail can be tough.
• Rough Texture – Picatinny slots can be like a cheese grater on your bare skin if left uncovered
• Heavy – All of the extra material that makes the rail system strong, also makes it heavy

Note: There is a similar design to Picatinny that is called “Weaver”. It is easy to get these two confused, however, they are different mounting surfaces. Ensure that if you are looking at a rail similar in nature to picatinny, verify which specification it actually is.

M-LOK

The Modular Lock System from Magpul is a bit more complicated, but still simple to use. The slots on the rail look like skinny ovals. A M-LOK mounting accessory now has two screws with a similar shaped type of lock nut. The lock nut stays on the screws at all times. Turn the screws so that the nut can fit through the slot. Now, turn the screws again so that the nuts are perpendicular to the slot. Now tighten. The nuts clamp onto the inside of the rail and tighten down your accessory as you tighten down your screws. Bam, your M-LOK accessory is now mounted onto the M-LOK rail.

Notice the design of the M-LOK in this photo. The two nuts are able to be turned onto the screws that they are placed on. Simply turn them so that they line up into the slot, then turn them again so that they are perpendicular to the slot and you can start clamping the nuts onto the rail.

• Negative Space – Alright I’m going to say it..negative space. Are you turned on yet? You should be, because this term is what will pop up in any google search you do on M-LOK due to being of such importance within Mil-Requirements when designing and delivering M-LOK. Really though, it is a huge pro. It makes rails much less bulky due to not having to add anything to the rail to make the system but instead, cutting out holes
• Weight – Less bulk also means less weight. Something that someone like myself, a small female with small hands and not as many muscles as you big boys, loves in a hand rail.
• Direct Mount – Accessories are able to be directly mounted to the rail, thus not adding any bulk to the accessory and ensuring that it stays tight to the rail.
• Slim – The more slots, the more places that accessories can be mounted. M-LOK allows for multiple different places for accessories to be mounted without adding the bulk of more material.

• Learning Curve – M-LOK is a little more difficult to get the hang of and there are more parts to lose. However, once you get the trick of knowing when to twist the screws so that the nuts latch onto the rail and how to pull up when tightening, ensuring that those nuts don’t move, it’s easy peasy. Just make sure you don’t lose a nut inside the gun..speaking for a friend..wink wink.
• Nock Offs – While all things M-LOK are supposed to be licensed as well, there are still some crap options out there, such as plastic rail sections and incorrectly sized M-LOK pieces. This can make installation a pain. Ensure that any M-LOK product you get has the M logo on it from Magpul and isn’t plastic. Just stay away from non-aluminum rail sections, you’ll thank me later.

The Importance of Knowing Your Locking System

So why do we care? Well, any type of accessory that you buy will need to be compatible with the system that you’re mounting it to.

Picatinny mounting plates on accessories are pretty easy to spot due to the clamping bars on the sides of the accessory. All of the above accessories are set up to be mounted to picatinny rails including the old school KAC foregrip.

Optics that are being mounted on the top rail are pretty easy considering most top rails of firearms are 1913 picatinny. At this point, you just need to decide the height of the mount of your optic that you want, and if you want it to be attached with a tensioning lever, screws, or locking lugs.

Other accessories get a little more tricky. For instance, some accessories that you buy if you do not buy an adapter will only be able to be mounted onto picatinny. Thus, if you have a M-LOK handguard, you will then need to buy a picatinny section and mount it onto your handguard. If you do find the same accessory in M-LOK, buy that. Direct mounting on anything is always better than allowing for two things to come loose.

“I remember being at Fort Benning one year, and I was there with a group of people, and this sergeant came up to me, he said, “You’re Reed Knight, aren’t you?” I said, “Yeah, I am.” He said, “I just want to shake your hand,” he said, “I train thousands of people here in basic training in the shooting skills, and every time I get a shooter that does not qualify, I can give them one of your vertical pistol grips, and they always qualify afterwards. That one piece of gear has made more difference in people qualifying in military shooting than any other piece of gear that I’ve ever seen come through here.”-Mr. Knight

quote about that foregrip from an Interview with Mr. Knight on SmallArmsReview

In this photo is both M-LOK and Picatinny. The Magpul Hunter Stock has M-LOK sections on the stock’s for additional accessories. However, I wanted a bipod that could easily be detached. To do that I purchased a Picatinny rail section and mounted it via M-LOK enabling the quick detach picatinny adapter to be mounted onto the gun.

Things such as bipods that you may want to become quick detach (QD) also create some issues. Depending on your bipod, you may need to buy a Picatinny or M-LOK adapter that is compatible with your specific bipod. Many of these QD adapters, such as this one from American Defense Manufacturing, will only release from Picatinny so another section may need to be bought. If you don’t care for your bipod to be quick detach, simply buy a M-LOK Bipod Mount such as this one from Magpul.

In simple terms, the three things that you need to know is, what mounting system is my handguard? What mounting system does my bipod currently attach to? What system do I want it to be attached to? At that point, simply input those terms into google and you should find information for it.

Tips for Mounting Hardware

• When mounting optics onto the top picatinny rail add some lubrication to the rail, this will help with friction and keeping the optic tight.
• Push forward (to the muzzle of the gun) on your accessory when mounting. This will help with recoil and keeping the accessory tight.
• Witness mark your screws. This means that after tightening everything down, take a paint pen and mark on the screws and your rail in a line. This will show you if anything moves before you lose your accessory in the grass or wonder why you aren’t hitting where your optic says you should.

The Magpul furniture for the Remington 870 also features M-LOK, because who doesn’t want additional stuff on their shotgun such as a light? Note the two white lines on the Magpul branded screws for M-LOK accessories. Those white lines are known as witness marks. If those white lines no longer match up over time I know that something has come loose and the screws have shifted.

• If you are using a tensioning lever instead of screws, ensure that you adjust the lever so that it is TIGHT. Like so tight that you need to pull on it with paracord to loosen it and release the lever because your fingers aren’t strong enough (trust me it’s a trick). Too loose of a lever means your accessory will come loose during recoil.
• Vibra-tite or Loctite 242 are your friends. These are types of threadlocker that work great with items mounted on a firearm and undergoing recoil.
• Use the correct sized bit for the screws on your accessory. These screws and bits are often small, thus if you don’t use the correct size the screws and the bit can easily be stripped.

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It was not long ago that shooters had one of two choices when it comes to forend accessory systems: the proven, yet slightly heavy and snag prone Picatinny rails. Or a variety of proprietary mounting systems that are lighter, lower-profile and unique to one of a variety of manufacturers, each requiring different accessory mounts. Now that firearms owners find themselves twenty years deep into the 21st century, when it comes to accessory mounting on handguards, the decision tree for forend systems has two main branches: the veteran Picatinny rails and the modern M-LOK slots. So, which one is right for you? Let's take a look at the details surrounding both M-LOK vs Picatinny attachment systems.

Choices - M-LOK vs Picatinny 

Between the military, law enforcement and civilian shooters, there are millions of carbines and rifles in use in the United States. And with a heavy focus on usability and practicality, the AR-15 style rifle has grown into a modular weapons platform that can be used for a variety of applications ranging from competition shooting to home defense. Becoming a platform is an important process; attachments need a solid and universal system that the industry can support with mounting solutions. And on top of all that, it needs to be light enough to avoid front-end weight, which can cause fatigue.

I. M-LOK vs Picatinny - Details and Specifications

MIL-STD-1913 Picatinny Rail

With humble beginnings as an optic or sighting attachment system for rifles, development of a simple yet robust accessory mounting system for forend and handguard accessories started decades ago. Picatinny rail accessory attachment development began in the early 1990's and was finalized in 1995 as the MIL-STD-1913 accessory rail attachment system. The military, law enforcement and civilian shooting world finally had a standardized way to attach optics, sights, lights, lasers, night vision devices, bipods and other accessories made by manufacturers around the world.

Measurements:

• Picatinny locking slot width: 0.206 in (5.23 mm).

• Spacing of slot centers: 0.394 in (10.01 mm)

• Slot depth is 0.118 in (3.00 mm)

Magpul Modular Lock - M-LOK

Launching as part of the MOE system from Magpul around 2007, the M-LOK system uses an industry standard size slot system. In combination with accessory mounting systems that use a rotating internal lever that is loosened or tightened with a hex key, lights, foregrips and a host of other attachments are securely fastened in a slot on a handguard. The M-LOK system can save on unnecessary weight, reduce the outer diameter of the platform itself and has a smoother outer face, reducing the potential for snags on other gear in use by the operator.

Measurements:

• Slot length: 1.260 in

• Slot Width: 7mm (0.276 in) wide and

• Space between slits: 8 mm (0.315 in)

• Radius of the corners: 2.38 mm (0.094 in) approx

M-LOK Torque Specs:

• 4.0 N⋅m (35 lb-in) metal accessories to metal handguards.

• 1.7 N⋅m (15 lb-in) polymer or metal accessories to polymer handguards.

• 1.7 N⋅m (15 lb-in) polymer accessories to metal handguards.

II. M-LOK vs Picatinny - Attachment Methods

When it comes to mounting equipment to a forend or a handguard, there are several considerations that the end user should take into account:

• Quick detach capabilities - The need to add or remove a device quickly without the use of tools.

• Solid mounting and ease of use - The ability to easily add or remove a device, even under duress.

• Repeatability - Removing and installing an optical or aiming device while maintaining a zero on the same weapon system

III. M-LOK vs Picatinny - Handguard Profiles

Besides the ability to add and remove accessories, two of the biggest considerations when selecting an attachment system is weight and bulk. In general, M-LOK systems weigh less than their Picatinny counterparts because they don’t require the extra mass of external rails.

It may seem obvious at this point, but Picatinny rail systems require larger outer diameters than M-LOK systems. A quad rail (top, bottom and sides) requires space for the external rail as well as clearance for the equipment being attached. In comparison, since the M-LOK system does not utilize an external rail for attachment and does not require clearance for attaching devices, an M-LOK system can have a smaller overall outer diameter.

IV. M-LOK vs Picatinny - Final Thoughts

Much like the decisions that go into buying a firearm or any other piece of gear, there is no right or wrong answers when it comes to picking M-LOK vs Picatinny mounts. In most cases, an experienced shooter will own and use both attachment systems at some point over the course of their lifetime and will be able to judge accurately for themselves the pros and cons of M-LOK vs Picatinny accessory attachment systems.