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, Leica, Minox, Meopta, Nikon, Noblex (formerly Docter), Schmidt & Bender and Steiner. 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.
Swarovski SR rail The Swarovski SR rail (patented in 2002, introduced in 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.
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:
3⁄4 inch (19 mm) 7⁄8 inch (22 mm) 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. One scopes made for ring mounts, it is not uncommon to get ring marks when mounting the rings.
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