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 that clamp onto the scope tube via screw-tightened rings (similar to pipe shoes). 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.
Attachment interfaces for scope mounts vary according to weapon design and user choice. Traditionally scope mounts are fastened onto firearms via tapped screw holes (usually on the receiver) and/or clamps (onto the barrel or stock). Since the mid-20th century, dovetail rails, where the mount is slid over a straight dovetail bracket with an inverted isosceles trapezoid cross-section and fixed tight in position with clamping screws, became more common due to the ease of installation and removal. Later, the hexagonally cross-sectioned rail interface systems such as Weaver rail became popular and was later modified into the Picatinny rail in the early 1990s, which became the standardized military-use mounting interface for NATO troops in 1995. The Picatinny rail was officially replaced by the metrified NATO Accessory Rail for military use in 2009, although it remained popular in the civilian market for both scope and accessory mounting.
Scope mounts can be either one-piece (a single implement with multiple clamping rings) or multi-piece (usually two or more individual scope rings). These mounts are usually fastened with screws to specified tensions (which warrants the use of torque screwdrivers), but sometimes they are manually tightened via thumbscrews, and may even have Quick Release (QR) designs. As of 2020, the Picatinny rail is arguably the most widespread scope mounting standard for new firearms, although there are many proprietary and brand-specific types of mounts that can either be used with Picatinny rails, or as completely different design alternatives (see the section on Link between scope and firearm). Scope mounts may be offered by firearm and scope manufacturers, or bought as aftermarket accessories.
Integral scope mounts
Zeiss rail Among scopes for rail mounts, the 22.5-degree V-shaped Zeiss rail is the most prevalent standard. It was introduced in 1990. After the patent expired in 2008, compatible scopes have been offered from manufacturers such as Blaser,Blaser Infinity 2.8-20x50 IC vs Swarovski Z8i 2-16x50 – Rifles Scopes Expert Every Blaser [scope] comes with a Zeiss ZM/VM mounting rail [...] Leica, Minox, Meopta, Nikon,Nikon Sport Optics & Hunting Catalogue 2017 "Rail mount models (Zeiss Inner Rail Standard) are available (1-4x24 IL ZR and 2.5-10x50SF IL ZR" Noblex (formerly DocterDocter to Noblex – Optics info), Schmidt & BenderSchmidt & Bender – Main catalog 2016 and Steiner.Nighthunter Xtreme Riflescope Instruction Manual "Rail models work with standard rail bases for “Z" or Zeiss rails." It has therefore, in some sense, become the de facto industry standard for scope mounting rails. The system has so far seen most use on the European high end market.Zeiss ZM / VM Rifle Scope mounting rail – Optics info
Swarovski SR rail The Swarovski SR rail (patented in 2002,Patent AT480748T Application filed 9 June 2002 by Swarovski Optik]Patent US6901692B2 Application granted 7 June 2005]Patent DE50214644D1 Application granted 21 October 2010] introduced in 2005Swarovski catalog October 2005 The Swarovski SR rail is also used by Kahles, a Swarovski subsidiary.) has a flat rail with many "teeth" as recoil lugs, and is only offered on scopes from Swarovski and its subsidiary Kahles. It separates itself from the Zeiss rail in that it is not neither stepless nor self-centering.
S&B Convex rail A former competing standard was the halv-circle shaped Schmidt & Bender Convex rail also introduced in 2005. Schmidt & Bender after a few years changed to the Zeiss rail standard. In contrast to the Zeiss and Swarovski systems, the S&B Convex rail had the possibility to add a cant to the scope when mounting, such that the reticle is not horizontal to the ground.Schmidt & Bender catalogue "The convex hollow rail. Our hollow rail with a convex outer surface, offered on all Zenith models, is distinguished by elegant lines, and allows the use of reliable slide-in mount fasteners. This innovative rail also makes it possible to tilt the scope up to 1° to the left or to the right."
70-degree prism rail There is an older European system with an upside-down V-shape (70 degrees). This system has little widespread use today. The advantage of this system was that it at one time was offered by most European scope manufacturers, but the disadvantage was that the rail had to be drilled for a screw each time the eye relief was to be adjusted. All new standards for rail mounts have addressed this issue.
Ring mounts
Ring mounts usually consist of a base attached to the firearm and rings (usually two) attached to the sight. The rings are usually made of steel or aluminum. Common diameters on ring mounts are 25.4 mm (1 inch), 26 mm, 30 mm and 34 mm. There are big differences in the strength and ability of sustained precision on different assemblies. With weak cartridges such as .22 LR applied in light-use scenarios, a pair of skinny aluminium rings may work well, while firearms with very powerful recoil often combined with a heavy sight may require steel rings or thicker aluminum rings with recoil lugs to be used.
Sizes Scopes for ring mounts are available in many different sizes. The most common ones are:
1 inch (25.4 mm) 30 mm 34 mm
Some less common standards are:
26 mm – Some older European scopes 35 mm – Some IOR, Vortex and Leupold models 36 mm – Some Zeiss and Hensoldt models 40 mm – Some IOR models and Swarovski dS
Lapping For a ring assembly to grip evenly, it is important that the scope rings are circular and coaxial with the scope tube. On ring mounts that grip unevenly, the ring mount can be lapped to prevent uneven pressure when mounting.RifleShooter – How to Lap Scope Rings One scopes made for ring mounts, it is not uncommon to get ring marks when mounting the rings.
Ring inserts There are insert rings on the market which allows for mounting a scope inside a ring mount of a larger diameter. An example could be to mount a scope with a 1-inch (25.4 mm) tube in a 30 mm mount using a plastic insert.
There are also special ring mounts in the market with circularly shaped ring inserts made to provide stress free mounting without lapping, with Burris Signature Rings and Sako Optilock Rings as two well-known examples. Burris Signature was introduced in 1995.History | Burris Optics A patent was applied for in 1994, and was granted in 1995.US5433010A – Self aligning optical gun sight mount with eccentric adjustment capabilities – Google Patents Sako Optilock has been sold since some time in the early 2000s.Internationaler Silhouettenclub – Visiereinstellungen The trade name Optilock was registered in the US in December 1997, and has been marketed in the US since December 2001.Trademark Electronic Search System (TESS) – 77509718 In 2000, Sako was sold to Beretta Holding. In 2002, Burris was also sold to Beretta Holding, and thus Burris and Sako got the same owners. Burris' original patent for the rings with the circular insertes was considered to have expired in 2014, and as of 2020 is listed as "definitely expired".
In 2015, XTR Signature Rings was launched as a further development of the Burris Signature series. The XTR variant differs in that it has two circular cavities per ring assembly versus one. A patent for the XTR Signature Rings was applied for in 2016, and was granted to Burris in 2019.US10415934B2 – Self-aligning optical sight mount – Google Patents
Mounts for compact sights
Many reflex sights (e.g. red dot sights) and holographic sights have proprietary mounts.Footprints/Mounting Standards on Red Dot Sights – Optics info
Aimpoint Acro rail: A dovetail rail for attaching a sight via a clamping mechanism, and with a 4 mm wide straight recoil lug groove. The dovetail is approximately 16.5 mm wide, and is radiused so as not to have any sharp edges. The mount is compact enough to be used on pistols, as well as rifles and shotguns. Launched in 2019 together with the sights Aimpoint Acro P-1 and C-1. Also used on Aimpoint Acro C-2 and P-2, as well as Steiner MPS. Aimpoint Micro standard: First introduced in 2007 on the small tube sight variants of Aimpoint, but today used by other manufacturers as well. Popular on rifles and shotguns, but not on handguns due to its size. The mounting standard uses four screws and one cross slot acting as a recoil lug. Used on red dot sights such as Aimpoint Micro, Vortex Crossfire, Sig Sauer Romeo 4 & 5, and some Holosun Paralow variants. Aimpoint CompM4 mount: Launched in 2007 with the Aimpoint CompM4 sight. The sight is attached to the mount via two M5 screws from the underside, and the mount has a transverse groove acting as a recoil lug. The Aimpoint Comp line was launched in 1993. The predecessor of the CompM4, CompM2, had a 30 mm ring mount and was introduced in the American military in 2000. Some manufacturers have copied the M4 mount system, but it has mainly been used by Aimpoint.Aimpoint Comp M4 review C-More standard: A mounting standard introduced by C-More Sights. Uses two screws and two circular notches acting as recoil lugs. Used on red dot sights such as Delta Optical MiniDot, Kahles Helia, Vortex Razor and Sig Sauer Romeo3. Docter/Noblex standard: The mounting pattern which through the 2010s was used by the largest number of manufacturers, perhaps due to the wide range of aftermarket mounts available. The mounting standard uses two screws and four circular notches acting as recoil lugs. Used on red dot sights such as Docter/Noblex sights, Burris Fastfire, Vortex Viper, Leica Tempus, etc. Shield standard: A proprietary standard used by Shield Sights. Similar in shape to the Noblex/Docter footprint, but with other dimensions. In addition to the Shield red dot sights, it is also used on the Leupold Delta Point Pro. Trijicon RMR/SRO-standard: Has two screw holes, and two shallow circular notches acting as recoil lugs. Mainly used on the Trijicon RMR and SRO red dot sights, as well as on some Holosun sights. Other: Some notable red dot sights which have unique footprints not compatible with any of the above are Sig Sauer Romeo 1, Holosun Paralow 403A, Holosun 509T and Swampfox Kraken MRDS. There also exists reflex sights for ring mounts (e.g. Aimpoint CompM2 with a 30 mm tube) or with an integrated Picatinny base.
Link between scope and firearm
Bases By bases, is usually meant an interconnecting part between the scope and the firearm. For example, a base may have a picatinny attachment on the underside, while the upper side may have either a ring (e.g. 30 mm) or rail mounting (e.g. Zeiss rail). On some assemblies, the upper and lower parts of the base are separate parts that must be screwed together and fastened to a specified torque.Scope & Rifle Torque Specs Database | Tactec A base can thus sometimes constitute a complete scope mount assembly, but is most often used to refer to the lower part of a two-part scope mount assembly.
The firearm interface which sits on the firearm and to which the scope mount is attached is often called the base or rail.
Some types of bases are:
Standard mounts Picatinny rail: Standardized slot distances. Weaver rail: Varying width between the slots.
Proprietary and brand specific mounts Claw mount. Several types, for example Suhl Claw Mounts,Suhl Claw Scope Mounts – Optics-Trade Ziegler ZP mount, and others.