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M-LOK, for Modular Lock, is a
firearm A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions). The first firearms originate ...
rail interface system developed and patented by Magpul Industries. The license is free-of-charge, but subject to an approval process. M-LOK allows for direct accessory attachment onto the "negative space" (hollow slot) mounting points, and is a competing standard to VLTOR's
open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...
d KeyMod system for replacing the ubiquitous
Picatinny rail The 1913 rail (MIL-STD-1913 rail) is an American rail integration system designed by Richard Swan that provides a mounting platform for firearm accessories. It forms part of the NATO standard STANAG 2324 rail. It was originally used for mount ...
in some applications. Both M-LOK and KeyMod enable the user to have a slimmer, lighter, smoother and more fenestrated
handguard A barrel shroud is an external covering that envelops (either partially or full-length) the barrel of a firearm to prevent unwanted direct contact with the barrel (e.g. accidental collision with surrounding objects or the user accidentally touch ...
/ fore-end with accessories and gadgets mounted only where needed as compared to a Picatinny handguard, which typically has whole length rail slots, resulting in a heavier weight, bulkier handguard and poorer
barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden stave (wood), staves and bound by wooden or metal hoops. The word vat is often used for large containers ...
ventilation, resulting in the barrel overheating more quickly. The M-LOK system can be seen as an evolution of the Magpul Original Equipment (MOE) system, but the two are not fully compatible. Though newer M-LOK accessories can be used on older MOE slot handguards if an adaptor plate is used, there is no adaptor available for using older MOE accessories on the newer M-LOK handguards.


History

A prototype of the MOE slot was revealed by Magpul in late 2007 together with their Masada Concept Rifle (which would later be known as the Adaptive Combat Rifle). Magpul released the MOE slot system in 2008 as a feature on their MOE handguards, and at the same time compatible accessories such as Picatinny rail sections, direct MOE mounted light mounts, grips, bipod studs, etc. were released. The MOE slot standard was never officially released, and a drawback to the system was that the rear side of the panel had to be accessed in order to mount accessories, limiting its application. The MOE slot system uses a weld nut which has to be placed manually on the inside of the handguard before mounting, making the slot system unsuited for applications such as free-floating handguards. Also, depending on the accessory item, the spacing increments between the MOE slots were not small or uniform enough to adjust the desired placement of accessories. Acknowledging shortcomings of the MOE systems, Magpul drafted M-LOK as a new and improved mounting standard which was released in 2014 replacing the existing MOE slot. The M-LOK rail specification included
metric Metric or metrical may refer to: Measuring * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics ...
dimensions instead of imperial, and utilizes a T-slot nut capable of only 90-degree rotation, reinforced by thread-locking fluid, making it suited for applications on free-floating handguards. It was designed to work with both metal and polymer parts. In 2016, Colt Canada developed and released the Modular Rail Rifle (MRR) that uses a monolithic upper receiver with the M-LOK attachment system. KeyMod and M-LOK handguards from various manufacturersIn 2017, several companies produce M-LOK handguards as well as accessories like Picatinny rail strips,
vertical foregrip A vertical forward grip or foregrip is a vertical pistol grip mounted on the forearm (firearm component), fore-end of a long gun, long-barrel firearm, designed for grasping by the frontal support hand (or "off hand"). Use Forward grips aid i ...
s,
bipod A bipod is a V-shaped portable attachment that helps support and steady a device, usually a weapon such as a long gun or a mortar. The term comes from the Latin prefix and Greek root , meaning "two" and "foot" respectively. Bipods are design ...
s, sling adaptors, and
flashlight A flashlight (US English) or electric torch (Commonwealth English), usually shortened to torch, is a portable hand-held electric lamp. Formerly, the light source typically was a miniature incandescent light bulb, but these have been displaced ...
mounts. In 2017, a summary report of testing conducted by NSWC-Crane for
USSOCOM The United States Special Operations Command (USSOCOM or SOCOM) is the unified combatant command charged with overseeing the various special operations component commands of the United States Army Special Operations Command, Army, United Stat ...
indicated that, while comparable in endurance and rough handling testing, M-LOK greatly outperformed Keymod in repeatability, drop testing and failure load testing. In 2018, the ''Upper Receiver Group-Improved'' (URG-I) is a U.S. Army Special Operations Command (USASOC) program to further improve the durability and reliability of the SOPMOD Block II by introducing additional component improvements. First fielded in the same year, the main improvements are the lighter Geissele Mark 16 free-float rail that incorporates M-LOK as the mounting method and a Daniel Defense cold hammer-forged barrel that returns to the lighter "government" profile contour as well as a mid-length gas system. Used on the M4A1 carbines by ASOC then MK18 URG-I variant CQBRs by AFSOC.


Licensing

While M-LOK is licensed free-of-charge, it is not
open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...
, and thus manufacturers must acquire a license from Magpul before making products using the M-LOK standard. Magpul claims this gives them more control in assuring that all M-LOK products are made to specifications ensuring compatibility. Program participation is open to any interested manufacturer. Note that although Magpul describes the license as a "free license", the meaning does not match the more common meaning originally established in computer circles. The computer "free license" refers to a freedom to use,Open Definition 2.1
on opendefinition.org ''"This essential meaning matches that of “open” with respect to software as in the Open Source Definition and is synonymous with “free” or “libre” as in the Free Software Definition and Definition of Free Cultural Works."''
while Magpul only conditionally offers the license for free (analogous to a
source-available Source-available software is software released through a source code distribution model that includes arrangements where the source can be viewed, and in some cases modified, but without necessarily meeting the criteria to be called ''open-source ...
freeware Freeware is software, often proprietary, that is distributed at no monetary cost to the end user. There is no agreed-upon set of rights, license, or EULA that defines ''freeware'' unambiguously; every publisher defines its own rules for the free ...
). NATO standards conform military issued assault rifles like the CAR 816 have semi-automatic only export versions featuring M-LOK rails on the handguard to better meet civilian market preferences in the United States.


Technical specifications


Rail specifications

The slot dimensions (used on handguards, etc.) are available on the web. The slots provide
metric Metric or metrical may refer to: Measuring * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics ...
length intervals, and accessories can be mounted either within a slot or bridging between slots, making it possible to adjust the position of accessories in smaller intervals than the length of the slot. The slots on an M-Lok handguard are approximately long and wide and space from each other. The radius of the corners is approximately .


Attachment specifications

The quarter-turn T-slot nuts have different
torque In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...
specifications depending on the handguard material: * for attaching metal accessories to metal handguards. * for attaching polymer or metal accessories to polymer handguards. * for attaching polymer accessories to metal handguards. Attachment screws made by many U.S. manufacturers are often either #8-32 TPI or 10-24 TPI UNC threads, which respectively have major thread diameters of 0.1640 inches and 0.1900 inches (4.166-0.794 mm and 4.826-1.058 mm expressed in metric designation). Many M-LOK screws on the international market instead use either M4 or M5 metric threads to reduce cost. The tool required for mounting, in addition to the thread size, also depends the screw head type. Hex keys are used extensively in the firearms industry, but metric and imperial hex keys as a general rule are not compatible. It is possible to damage the tool and screw by selecting a tool that is too small for the fastener, which can be done by using an imperial tool on a metric fastener, or the converse. An exception to this is 4 mm hex keys, which are almost the exact same size as . In many industries, this makes hex keys preferred for consumer products because end users can successfully use an imperial key on a metric fastener, and vice versa. While screw and slot dimensions are available on the web, the T-slot nut dimensions are currently under review by the
US State Department The United States Department of State (DOS), or simply the State Department, is an executive department of the U.S. federal government responsible for the country's foreign policy and relations. Equivalent to the ministry of foreign affairs o ...
to determine whether it should be regulated by ITAR, and until it is clarified drawings are only available to US citizens. File:M-LOK 1.png, M-LOK handguard and attachment parts File:M-LOK dimensions.jpg, M-LOK approximate slot dimensions. (Primary measurements in millimeters, inches in parentheses.)


See also

* KeyMod—competing standard open standard design to M-LOK for mounting accessories * NATO Accessory Rail—further development from the MIL-STD-1913 *
Picatinny rail The 1913 rail (MIL-STD-1913 rail) is an American rail integration system designed by Richard Swan that provides a mounting platform for firearm accessories. It forms part of the NATO standard STANAG 2324 rail. It was originally used for mount ...
(MIL-STD-1913)—improved and standardized version of the Weaver mount. Used for both for
scope mount Scope mounts are rigid implements used to attach (typically) a telescopic sight or other types of optical sights onto a firearm. The mount can be made integral to the scope body (such as the Zeiss rail) or, more commonly, an external fitting t ...
s, and for accessories (such as extra sling mounts, vertical grips, bipods etc.) Major popularity in the civilian market. *
Rail Integration System file:Dovetail.jpg, A dovetail rail on a rifle receiver for scope mount, mounting a Sight (device), sight A rail integration system (RIS; also called a rail accessory system (RAS), rail interface system, rail system, mount, base, gun rail, or si ...
—generic term for a system for attaching accessories to small
firearm A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions). The first firearms originate ...
s * SOPMOD * UIT rail—an older standard used for mounting slings particularly on competition firearms *
Weaver rail mount A Weaver rail mount is a system to connect telescopic sights (often via a scope mount) and other accessories to firearms and certain crossbows. It uses a pair of parallel rails and several slots perpendicular to these rails. The later Picatinny ...
—early system used for scope mounts, still has some popularity in the civilian market * Zeiss rail—a ringless scope mounting standard


References


External links

* {{Firearm accessories mounting standards Firearm components Mechanical standards