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| M-LOK | |
|---|---|
.svg) | |
| Type | Attachment System |
| Place of origin | United States |
| Production history | |
| Designer | Magpul Industries |
| Designed | 2007–2014 |
| Produced | 2014–present |
M-LOK, forModular Lock, is afirearmrail interface system developed and patented byMagpul 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'sopen sourcedKeyMod system for replacing the ubiquitousPicatinny rail in some applications.[1] Both M-LOK and KeyMod enable the user to have a slimmer, lighter, smoother and morefenestratedhandguard/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 poorerbarrel 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.
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 theAdaptive 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 aweld nut which has to be placed manually on the inside of the handguard before mounting, making the slot system unsuited for applications such asfree-floating handguards[citation needed]. 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 includedmetric dimensions instead ofimperial, and utilizes aT-slot nut capable of only 90-degree rotation, reinforced bythread-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 monolithicupper receiver with the M-LOK attachment system.[2]
In 2017, several companies produce M-LOK handguards as well as accessories like Picatinny rail strips,vertical foregrips,bipods,sling adaptors, andflashlight mounts.[3][failed verification]
In 2017, a summary report of testing conducted byNSWC-Crane forUSSOCOM indicated that, while comparable in endurance and rough handling testing, M-LOK greatly outperformed Keymod in repeatability, drop testing and failure load testing.[4]
In 2018, theUpper Receiver Group-Improved (URG-I) is aU.S. Army Special Operations Command (USASOC) program to further improve the durability and reliability of theSOPMOD 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 variantCQBRs byAFSOC.
While M-LOK is licensed free-of-charge, it is notopen source, 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.[5]
Note that although Magpul describes the license as a "free license", the meaning does not match themore common meaning originally established in computer circles. The computer "free license" refers to a freedom to use,[6] while Magpul only conditionally offers the license for free (analogous to asource-availablefreeware).
NATO standards conform military issued assault rifles like the CAR 816 have semi-automatic onlyexport versions featuring M-LOK rails on the handguard to better meet civilian market preferences in the United States.[7][8][9]
The slot dimensions (used on handguards, etc.) are available on the web.[10] The slots providemetric 20 mm (0.79 in) 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 32 mm (1.260 in) long and 7 mm (0.276 in) wide and space 8 mm (0.315 in) from each other. The radius of the corners is approximately 2.38 mm (0.094 in).[10][11][12]
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The quarter-turnT-slot nuts have differenttorque specifications depending on the handguard material:
Attachment screws made by many U.S. manufacturers are often either #8-32 TPI or 10-24 TPIUNC 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 M5metric 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 as5⁄32 in (3.97 mm). In many industries, this makes4.0 mm (5⁄32 in) hex keys preferred for consumer products because end users can successfully use an imperial key on a metric fastener, and vice versa.
| Hex key spanner (wrench) size | |||||
|---|---|---|---|---|---|
 Thread type |  Socket head cap screw |   • Flat head counter- sunk cap screw • Button head cap | |||
| M4 | 3 mm | 2.5 mm | |||
| M5 | 4 mm | 3 mm | |||
| #8-32 | 9⁄64" (3.57 mm) | 3⁄32" (2.38 mm) | |||
| #10-24 | 5⁄32" (3.97 mm) | 1⁄8" (3.18 mm) | |||
While screw and slot dimensions are available on the web, the T-slot nut dimensions are currently under review by theUS State Department to determine whether it should be regulated byITAR, and until it is clarified drawings are only available toUS citizens.
Media related toM-LOK at Wikimedia Commons