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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 [1] ) is a generic term for a standardized system for attaching accessories to firearms. Rail systems are straight mounting brackets (usually made of strips of metal or polymer) on the gun's receiver, handguard, or fore-end stock to allow sliding or 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 reliefs on gun sights.
Firearm accessories commonly compatible with or intended for rail systems include tactical lights, laser sights, vertical forward grips, telescopic sights, holographic sights, reflex sights, backup iron sights, bipods/tripods, slings, and bayonets.
The common types of rail systems for firearms are the dovetail rail [2] [3] (including the Soviet variant known as the Warsaw Pact rail), the Weaver rail, [4] the Picatinny rail, the SOPMOD, and the M-LOK. [5] [6] [7] [8] 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.
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. [9]
Rail systems are usually based on the handguard 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.
On the Kalashnikov rifles, 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 out a dove tail slot for the placement of a gun sight's parts.
Optics such as telescopic sights, reflector sights, holographic sights, red dot magnifiers, night vision sights, or thermal sights may be placed between the iron sights. 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.
Most RIS equipment is compatible with one or more of the most common rail systems, all of which are broadly similar:
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.
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 handguards. 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.
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. [1]
The most common weapons to have rails are individual firearms, particularly long guns and service rifles such as the rifle, carbine, submachine gun, personal defense weapon, shotgun, designated marksman rifle, sniper rifle, and squad automatic weapon, though some larger or crew-served weapons such as the heavy machine gun, anti-materiel rifle, and rocket launcher have been designed or refreshed to include rails for compatibility. Even ranged weapons that are not firearms, such as bow and arrow, crossbow, airsoft gun, and paintball marker.
HMGs have started to include and use rail sections and options for attachments of optics. Civilian clone rifles are the main weapons to adopt this, while crossbows, [11] hunting rifles, shotguns, and handguns may be produced with rail sections either attached and/or made structurally as part of the actual firearm. Airsoft and paintball clone weapons may also have rails.
The Colt Canada C7 and C8 are a Canadian family of service rifles, manufactured by Colt Canada, having similar design and function to the Colt M16A3.
The Springfield Armory M1A is a semi-automatic rifle made by Springfield Armory, Inc., beginning in 1971, based on the M14 rifle, for the civilian and law enforcement markets in the United States. "M1A" is a proprietary name for Springfield Armory's M14-pattern rifle. Early M1A rifles were built with surplus G.I. parts until Springfield Armory, Inc. began manufacturing their own. Robert Reese bought Springfield Armory from Elmer Ballance, and moved the manufacturing to Geneseo Ill in 1974.
The Heckler & KochXM8 is a lightweight assault rifle system developed from the late 1990s to early 2000s. The rifle was designed by German small arms manufacturer Heckler & Koch (H&K), and shares design and engineering with their G36 rifle.
The Picatinny rail, which meets MIL-STD-1913 rail, is an American design rail integration system that provides a mounting platform for firearm accessories. It forms part of the NATO standard STANAG 2324 rail. It was originally used for mounting of scopes atop the receivers of larger caliber rifles.
The Ares Defense Shrike 5.56 is an air-cooled, dual-feed rifle for semi or full-auto configurations that fires the 5.56×45mm NATO cartridge. The Shrike 5.56 can be supplied as a complete weapon, or as an upper receiver “performance upgrade kit” to existing M16-type service rifles and carbines. it is named after the Shrike, a carnivorous passerine bird, and was designed by Geoffrey Herring.
The Ruger 10/22 is a series of semi-automatic rifles produced by American firearm manufacturer Sturm, Ruger & Co., chambered for the .22 Long Rifle rimfire cartridge. It uses a patented 10-round rotary magazine, though higher capacity box magazines are also available. The standard carbine version of the Ruger 10/22 has been in production continuously since 1964, making it one of the most successful rimfire rifle designs in history, with numerous third party manufacturers making parts and accessories for upgrading and customization. The 10/22's aftermarket is so prolific that a complete 10/22 can be built without using any Ruger-made components.
A Weaver rail mount is a system to connect telescopic sights and other accessories to firearms and certain crossbows. It uses a pair of parallel rails and several slots perpendicular to these rails.
The Z-M LR-300 is an American rifle designed by gunsmith Allan Zitta and manufactured by Z-M Weapons. The model name LR-300 stands for Light Rifle and 300 is for 300 meters, which is regarded by the manufacturer as the effective range of the rifle with a standard 55 gr (3.6 g) FMJ bullet. The design is based on the AR-15, M16 and C7 rifles, but has a unique semi-direct gas impingement system and a folding stock option.
Daewoo Precision Industries K2 assault rifle is the standard service rifle of the South Korean military. It was developed by the South Korean Agency for Defense Development and manufactured by SNT Motiv and Dasan Machineries. Shoulder-fired and gas-operated, the K2 is capable of firing both 5.56×45mm NATO and .223 Remington ammunition; however, using .223 Remington is only recommended for practicing for short distance.
The SG 550 is an assault rifle manufactured by SIG Sauer AG in Switzerland. "SG" is an abbreviation for Sturmgewehr. The rifle is based on the earlier 5.56×45mm NATO SIG SG 540.
The SR-3 Vikhr is a Russian 9×39mm compact assault rifle. It was developed by A. D. Borisov, V. N. Levchenko and A. Tyshlykov at TsNIITochMash in the early 1990s and was manufactured in 1994. Heavily based on the AS Val, but lacks an integral suppressor, has a newly designed folding stock and charging handle for ease of concealed carry. The abbreviation "SR" stands for spetsialnaya razrabotka — special development.
A barrel shroud is an external covering that envelops the barrel of a firearm, to prevent unwanted direct contact with the barrel. Moving coverings such as pistol slides, fore-end extension of the gunstock/chassis that do not fully encircle the barrel, and the receiver of a firearm itself are generally not described as barrel shrouds, though they can functionally act as such.
The karabinek wz. 1996 Mini-Beryl is a Polish compact assault rifle (carbine) derived from the FB Beryl service rifle and chambered for 5.56×45mm. It was developed in parallel with the wz. 1996 Beryl by the "Łucznik" Arms Factory in Radom and introduced into service with the Polish Armed Forces in 1997 as the 5,56 mm karabinek krotki wz. 1996.
The NATO Accessory Rail (NAR), defined by NATO Standardization Agreement (STANAG) 4694, is a rail interface system standard for mounting accessory equipment such as telescopic sights, tactical lights, laser aiming modules, night vision devices, reflex sights, foregrips, bipods and bayonets to small arms such as rifles and pistols.
The IWI Galil ACE is a series of assault rifles and battle rifles originally developed and manufactured by Israel Weapon Industries (IWI). It is produced in three different calibres: 5.56×45mm NATO, 7.62×39mm and 7.62×51mm NATO.
KeyMod is a universal interface system for firearm accessory components designed to supersede the MIL-STD-1913 "Picatinny" accessory rails. 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 sourced in the public domain for adoption by the entire firearms accessory industry. The name "KeyMod" was coined by Eric Kincel following the naming trend of other VLTOR accessories with the suffix "Mod" meaning modular, and "Key" being a reference to the key-hole profile of the mounting slots.
M-LOK, for Modular Lock, is a firearm rail interface system developed and patented by Magpul Industries. The license is free-of-charge, but subject to an approval process.
The UIT rail, also known as Anschutz rail, is a standard used for mounting slings and other gun accessories in competition shooting, and is essentially a T-slot track shaped aluminium extrusion profile accepting attachments in the form of T-slot nuts, or similar.
A dovetail rail or dovetail mount can refer to several types of sliding rail system found on firearms, primarily for mounting telescopic sights. Colloquially, the term dovetail rail usually refer to any straight mounting bracket with an inverted trapezoid (dovetail) cross-section running parallel to the bore for mounting a scope or diopter sight to a rifle. These are sometimes also called "tip-off" mounts, and allow the user to easily take on or off the sight. Dovetail mount can also refer to a dovetail track running perpendicular to the bore.
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 or, more commonly, an external fitting that clamp onto the scope tube via screw-tightened rings. The scope and mount are then fastened onto compatible interfaces on the weapon. Words such as mounts and bases are used somewhat loosely, and can refer to several different parts which are either used together or in place of each other as ways to mount optical sights to firearms.