A dovetail rail on a rifle receiver for mounting a sight A rail integration system (RIS; also called a rail accessory system (RAS), rail interface system, rail system, mount, base, gun rail, or simply a rail) is a generic term for any

standardized Standardization (American English) or standardisation (British English) is the process of implementing and developing technical standards based on the consensus of different parties that include firms, users, interest groups, standards organiza ...

attachment system for mounting

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 ...

accessories via bar-like straight brackets (i.e. "rails") often with regularly spaced slots. Rail systems are usually made of strips of metal or polymer

screw A screw is an externally helical threaded fastener capable of being tightened or released by a twisting force (torque) to the screw head, head. The most common uses of screws are to hold objects together and there are many forms for a variety ...

-fastened onto the gun's receiver,

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 ...

, or fore-end stock to allow variable-position attachments. An advantage of the multiple rail slots is the moveable positions to adjust for optimal placement of each item for a user's preferences, along with the ability to switch different items at different placements due to varying

eye relief {{unref, date=June 2023 The eye relief of an optical instrument (such as a telescope, a microscope, or binoculars) is the distance from the last surface of an eyepiece within which the user's eye can obtain the full viewing angle. If a viewer's eye ...

s on gun sights. Firearm accessories commonly compatible with or intended for rail systems include

tactical light A tactical light or weapon light is a flashlight used in conjunction with a firearm to aid low-light target identification, allowing the user to simultaneously aim a weapon and illuminate the target. Tactical lights can be handheld or mounted to ...

s, laser sights, vertical forward grips,

telescopic sight A telescopic sight, commonly called a scope informally, is an optical sighting device based on a refracting telescope. It is equipped with some form of a referencing pattern – known as a ''reticle'' – mounted in a focally appropriate p ...

s, holographic sights,

reflex sight A reflector sight or reflex sight is an optical sight that allows the user to look through a partially reflecting glass element and see an aiming point or some image (helping to aim the device, to which the sight is attached, on the target) sup ...

s, backup

iron sights Iron sights are a system of physical alignment markers used as a sighting device to assist the accurate aiming of ranged weapons such as firearms, airguns, crossbows, and bows, or less commonly as a primitive finder sight for optical telescop ...

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 ...

tripod A tripod is a portable three-legged frame or stand, used as a platform for supporting the weight and maintaining the stability of some other object. The three-legged (triangular stance) design provides good stability against gravitational loads ...

s, slings, and

bayonet A bayonet (from Old French , now spelt ) is a -4; we might wonder whether there's a point at which it's appropriate to talk of the beginnings of French, that is, when it wa ... , now spelt ) is a knife, dagger">knife">-4; we might wonder whethe ...

s. The common types of rail systems for firearms are the

dovetail rail A dovetail joint or simply dovetail is a joinery technique most commonly used in woodworking joinery (carpentry), including furniture, cabinets, log buildings, and traditional timber framing. Noted for its resistance to being pulled apart, a ...

(including the

Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

variant known as the

Warsaw Pact The Warsaw Pact (WP), formally the Treaty of Friendship, Co-operation and Mutual Assistance (TFCMA), was a Collective security#Collective defense, collective defense treaty signed in Warsaw, Polish People's Republic, Poland, between the Sovi ...

rail), the Weaver rail, the

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 ...

, the

SOPMOD The Special Operations Peculiar MODification (SOPMOD) kit is an accessory system for the M4A1 carbine, CQBR, FN SCAR Mk 16/17, HK416 and other weapons used by United States Special Operations Command (USSOCOM) special forces units, though i ...

, the

KeyMod KeyMod is a universal interface system for firearm accessory components. The concept was first created by VLTOR Weapon Systems of Tucson, Arizona, and released through Noveske Rifleworks of Grants Pass, Oregon, before being published Open-source so ...

and the

M-LOK M-LOK, for Modular Lock, is a firearm Rail Integration System, 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 ...

. There are also various non-military designs used in shooting sports to attach slings and bipods such as the UIT rail, Zeiss rail and Freeland rail.

History

Original rails were a raised metal strip with the sides undercut, less standardized than the dovetail design, to allow hardware to slide on and be secured by means of compression only.

Design

file:KeyMod and M-LOK handguards.png,

and

handguards from various manufacturers Rail systems are usually based on the

of a weapon and/or the upper receiver. Modern pistols usually have rail systems on the underside of the barrel. Rails on rifles usually start at the top dead center ("12 o'clock"), with other common placements at the bottom 180° ("6 o'clock") and on the sides at 90° ("3 o'clock" and "9 o'clock"); some rails are also diagonal at 45° angles as opposed to 90° angles, though these are less common. There may be additional attachment rails or holes at each 45° angle position running partially or entirely the length of the handguard. A Romanian PSL rifle with a Warsaw rail On the

Kalashnikov rifle Kalashnikov rifles (), also known as the AK platform, AK rifles, or simply the AK, are a family of assault rifles based on Mikhail Kalashnikov's original design. They are officially known in Russian as ''avtomat Kalashnikova'' (), and informally ...

s, the Warsaw rail is attached to the left side of the receiver when viewed from the rear. With more modern versions adding Picatinny style rails onto the sides of the handguards of the rifles for the mounting of additional equipment. Due to updating equipment, both styles may be found on some Warsaw Pact weapons. Modern-designed firearms often include rails made into the body, instead of being an added-on modification. Older firearms may need permanent modifications of having holes drilled and tapped for screw threads to fasten the rail sections to the firearm. This is easier than

milling Milling may refer to: * Milling (minting), forming narrow ridges around the edge of a coin * Milling (grinding), breaking solid materials into smaller pieces by grinding, crushing, or cutting in a mill * Milling (machining), a process of using ro ...

out a dove tail slot for the placement of a gun sight's parts. Optics such as

reflector sight A reflector sight or reflex sight is an optical sight that allows the user to look through a partially reflecting glass element and see an aiming point or some image (helping to aim the device, to which the sight is attached, on the target) sup ...

s, holographic sights,

red dot magnifier A sight magnifier is an optical telescope that can be paired with a non-magnifying optical sight on a weapon to create a telescopic sight. They work with the parallel collimated reticle image produced by red dot sights and holographic weapon ...

s, night vision sights, or thermal sights may be placed between the

. The rail section may also come in various heights to help align equipment, which may align with the original iron sights inline or below an illuminated optic's center dot, ring or chevron. This is referred to as absolute or lower 1/3 co-witness respectively. In addition to height variations some rail brackets may be offset at various degrees. 22.5°, 45°, and 90° are the most common, to place accessories and/or backup folding collapsible iron sights in such a way so that they are out of the line sight on the top of the firearm and/or to decrease the outer profile edge's size. Then, the original sights are a backup if the electronic optic should fail. The rail section may also move weapon-mounted lights forward so the light does not shine and reflect on the firearm directly, which may create shadows. The amount of rail space allows adjustment and personal optimization of each device and tool attached for the user. As designs have advanced the amount of space has succeeded in the actual need for placement space. Thus, rail covers and protectors may be added to prevent snagging on gear and/or plant foliage. Future rails systems may have the option of carrying batteries or other electricity systems to supply the needs of the increasing electronics mounted to aid the shooter. Standards are still being determined for these types of systems. An example of such is NATO standards NATO Accessory Rail which is the continued improvement and standardization of the Picatinny rail.

Types

file:M-LOK 1.png, A combination hand guard with

on top with

slots on the side, with two Sling (firearms), sling mounts and a five-slot Picatinny rail section accessory showing the mounting hardware Most RIS equipment is compatible with one or more of the most common rail systems, all of which are broadly similar: *

Dovetail rail A dovetail joint or simply dovetail is a joinery technique most commonly used in woodworking joinery (carpentry), including furniture, cabinets, log buildings, and traditional timber framing. Noted for its resistance to being pulled apart, a ...

: one of the earliest rail systems, relies primarily on friction from the side unit

set screw In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. A set screw is normally used without a nut (which disting ...

on the mounted accessory to stop longitudinal shifting *

Warsaw Pact rail Warsaw, officially the Capital City of Warsaw, is the capital and List of cities and towns in Poland, largest city of Poland. The metropolis stands on the Vistula, River Vistula in east-central Poland. Its population is officially estimated at ...

: a

-designed dovetail rail variant with cut-outs that allow quick side-mounting of optics (e.g.

PSO-1 file:Tigr pso 1 med.jpg, Russian PSO-1M2 current military issue 4×24 telescopic sight file:Pso-1onsvd.jpg, View through a PSO-1 telescopic sight mounted on an SVD rifle The PSO-1 (''Прицел снайперский оптический, Pritse ...

and USP-1) on Dragunov sniper rifles,

RPG-7 The RPG-7 is a portable, reusable, unguided, shoulder-launched, anti-tank, rocket launcher. The RPG-7 and its predecessor, the RPG-2, were designed by the Soviet Union, and are now manufactured by the Russian company Bazalt. The weapon has t ...

and

RPG-29 The RPG-29 "Vampir" is a Soviet Union, Soviet Reuse, reusable rocket-propelled grenade (RPG) launcher. Adopted by the Soviet Army in 1989, it was the last RPG to be adopted by the Soviet Armed Forces, Soviet military before the Dissolution of the ...

grenade launchers, as well as some versions of AKM and

AK-74 The AK-74 ( Russian: , tr. ''Avtomat Kalashnikova obraztsa 1974 goda'', lit. 'Kalashnikov assault rifle model 1974') is an assault rifle designed by small arms designer Mikhail Kalashnikov in 1974 as a successor to the AKM. While primarily ...

assault rifle An assault rifle is a select fire rifle that uses an intermediate cartridge, intermediate-rifle cartridge and a Magazine (firearms), detachable magazine.C. Taylor, ''The Fighting Rifle: A Complete Study of the Rifle in Combat'', F.A. Moyer '' ...

s and PK family machine guns. * Weaver rail: an early improvement design upon the dovetail rail, invented by William Ralph Weaver (1905–1975). This system is still popular in the civilian market. *

: the

mil-spec A United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washi ...

standardized rail system evolved from the Weaver rail. Also known as MIL-STD-1913, Picatinny rails date from the mid-1990s and have very strict dimensions and tolerance standards. The Picatinny has a rail of a very similar profile to the Weaver, but the slot width is 0.206 in (5.23 mm), and the spacing of slot centers is consistent at 0.394 in (10.01 mm). Many rail-grabber-mounted accessories can be used on either type of rail. The Picatinny locking slot width is and the spacing of slot centers is ."Picatinny Rails, Weaver Rails, What’s The Difference?"
Brownells Due to this, with devices that use only one locking slot, Weaver devices will fit on Picatinny rails, but Picatinny devices will not always fit on Weaver rails. * NATO Accessory Rail: a

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 ...

standardized upgrade from the Picatinny rail. *

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 ...

"negative space" (hollow slot) design introduced by VLTOR to replace the Picatinny rail for mounting accessories (except 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). *

: a

free license A free license or open license is a license that allows copyrighted work to be reused, modified, and redistributed. These uses are normally prohibited by copyright, patent or other Intellectual property (IP) laws. The term broadly covers '' fr ...

d "negative space" design introduced by

Magpul Industries Magpul Industries Corporation is an American designer and manufacturer of high-tech polymer and composite firearms accessories like M-LOK M-LOK, for Modular Lock, is a firearm Rail Integration System, rail interface system developed and pa ...

to compete with

. These systems are used primarily in the military and by firearm enthusiasts to improve the usability of the weapon, being accessorized quickly and efficiently without requiring the operator to field-strip the weapon. Basic systems such as small rails (20mm is standard) with holes machined in them to be screwed onto the existing hand-guard of a rifle can cost as little as US $25 to US $40. More advanced systems allow for numerous accessories to be mounted simultaneously and can cost upwards of US $200.

Compatibility

A drawing comparing Anschütz (left) and Freeland equipment rails (right) Adapters to other types of rail interfaces may be used for legacy issues and/or to change the surface texture, abrasiveness and/or overall outer circumference of the entire rails system for the fit of the hand. Dovetail, Weaver, and Picatinny are all outward or raised attachment surfaces, while M-LOK and KeyMod have smooth surfaces with different standards & styles of holes cut into their assemblies to place the attachment hardware internally. Both of these styles are often in the

s. All make the mounting and dismounting of these objects significantly easier. Items may be fastened by threaded bolts, requiring the use of a screwdriver or Allen wrench. Some tool-free variations of thumb screws or thumb nuts may have a threaded quick disconnect lever that pulls the hardware and plates together against the rails. During firearm recoil, the accessory may slide within that section of the rail. To avoid this, when tightening a slide, move the device forward in the placement slots and ensure that the section of the bolt is positioned against the vertical/forward section of the rail slots.

Adoption

Though not particularly common on firearms until the late 20th century, most modern firearms in military service and the civilian market have rail integration systems that may replace original parts. The prevalence of rails on modern firearms compared to past designs is largely owed to the increasing popularity and availability of attachments such as sights. The most common weapons to have rails are individual firearms, particularly long guns and service rifles such as the

rifle A rifle is a long gun, long-barreled firearm designed for accurate shooting and higher stopping power, with a gun barrel, barrel that has a helical or spiralling pattern of grooves (rifling) cut into the bore wall. In keeping with their focus o ...

carbine A carbine ( or ) is a long gun that has a barrel shortened from its original length. Most modern carbines are rifles that are compact versions of a longer rifle or are rifles chambered for less powerful cartridges. The smaller size and ligh ...

submachine gun A submachine gun (SMG) is a magazine (firearms), magazine-fed automatic firearm, automatic carbine designed to fire handgun cartridges. The term "submachine gun" was coined by John T. Thompson, the inventor of the Thompson submachine gun, to descri ...

personal defense weapon Personal defense weapons (PDWs) are a class of compact, magazine-fed automatic firearms that are typically submachine guns designed to fire rifle-like cartridges. Most PDWs fire a small-caliber (generally less than in bullet diameter), high-velo ...

shotgun A shotgun (also known as a scattergun, peppergun, or historically as a fowling piece) is a long gun, long-barreled firearm designed to shoot a straight-walled cartridge (firearms), cartridge known as a shotshell, which discharges numerous small ...

designated marksman rifle A designated marksman rifle (DMR) is a modern telescopic sight, scoped high-Accuracy and precision, precision rifle used by infantry in the designated marksman (DM) role. It generally fills the engagement effective range, range gap between a serv ...

sniper rifle A sniper rifle is a high-precision, long range shooting, long-range rifle. Requirements include high accuracy, reliability, mobility, concealment, and optics, for anti-personnel weapon, anti-personnel, anti-materiel rifle, anti-materiel and sur ...

, and

squad automatic weapon A squad automatic weapon (SAW), also known as a section automatic weapon or light support weapon (LSW), is a man-portable automatic firearm attached to infantry squads or sections as a source of rapid direct firepower. Weapons fulfilling th ...

, though some larger or

crew-served weapons A crew-served weapon is any weapon system that is issued to a crew of two or more individuals performing the same or separate tasks to run at maximum operational efficiency, as opposed to an individual-service weapon, which only requires one per ...

such as the

heavy machine gun A heavy machine gun (HMG) is significantly larger than light, medium or general-purpose machine guns. HMGs are typically too heavy to be man-portable (carried by one person) and require mounting onto a weapons platform to be operably stable or ...

anti-materiel rifle An anti-materiel rifle (AMR) is a rifle designed for use against military equipment, structures, and other hardware (materiel) targets. Anti-materiel rifles are chambered in significantly larger calibers than conventional rifles and are employed ...

, and

rocket launcher A rocket launcher is a weapon that launches an unguided, rocket-propelled projectile. History The earliest rocket launchers documented in imperial China consisted of arrows modified by the attachment of a rocket motor to the shaft a few i ...

have been designed or refreshed to include rails for compatibility. Even ranged weapons that are not firearms, such as

bow and arrow The bow and arrow is a ranged weapon system consisting of an elasticity (physics), elastic launching device (bow) and long-shafted projectiles (arrows). Humans used bows and arrows for hunting and aggression long before recorded history, and the ...

crossbow A crossbow is a ranged weapon using an Elasticity (physics), elastic launching device consisting of a Bow and arrow, bow-like assembly called a ''prod'', mounted horizontally on a main frame called a ''tiller'', which is hand-held in a similar f ...

airsoft gun Airsoft guns are air guns used in airsoft sports. They are a special type of low-power smoothbore guns designed to shoot Airsoft pellets, plastic pellets often colloquially (but incorrectly) referred to as "BB (ammunition), BBs", which are typ ...

, and

paintball marker A paintball marker, also known as a paintball gun, paint gun, or simply marker, is an air gun used in the shooting sport of paintball, and the main piece of paintball equipment. Paintball markers use compressed gas, such as carbon dioxide (CO2) ...

. HMGs have started to include and use rail sections and options for attachments of optics. Civilian clone

s are the main weapons to adopt this, while

hunting rifle A rifle is a long-barreled firearm designed for accurate shooting and higher stopping power, with a barrel that has a helical or spiralling pattern of grooves (rifling) cut into the bore wall. In keeping with their focus on accuracy, rifles ar ...

s, and

handgun A handgun is a firearm designed to be usable with only one hand. It is distinguished from a long gun, long barreled gun (i.e., carbine, rifle, shotgun, submachine gun, or machine gun) which typically is intended to be held by both hands and br ...

s may be produced with rail sections either attached and/or made structurally as part of the actual firearm.

Airsoft Airsoft, also known as survival game () in Japan where it was popular, is a team sport, team-based shooting sport, shooting game in which participants eliminate opposing players out of play by shooting them with airsoft pellets, spherical plast ...

and

paintball Paintball is a competitive sport, competitive team sport, team shooting sport in which players eliminate opponents from play by hitting them with spherical dye-filled gelatin capsules called Paintball equipment#Paintballs, paintballs that b ...

clone weapons may also have rails.

Notes

References

*
Magpul Industries - M-LOK DESCRIPTION AND FAQ DOCUMENT

KeyMod vs. M-Lok: The Next AR Rail Standard by Chris Baker, November, 19, 2014

KeyMod vs. M-LOK Modular Rail System Comparison, Presented by Caleb McGee, Naval Special Warfare Center Crane Division, 4 May 2017 full pdf on page
*
M-LOK vs KeyMod comparison 2017 MLok and KeyMod Comparison 3 years later 2017

External links

KeyMod vs. M-LOK comparison
{{Firearms Firearm components Mechanical standards

History

Design

Types

Compatibility

Adoption

See also

Notes

References

External links