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 slided 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.
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,[1] Leica, Minox, Meopta, Nikon,[2] Noblex (formerly Docter[3]), Schmidt & Bender[4] and Steiner.[5] 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.[6]
The Swarovski SR rail (patented in 2002,[7] [8] [9] introduced in 2005[10] The Swarovski SR rail is also used by Kahles, a Swarovski subsidiary.[11]) 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.
A former competing standard was the halv-circle shaped Schmidt & Bender Convex rail[4] 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.[12]
There is an older European system with an upside-down V-shape (70 degrees).[13] 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.[14] All new standards for rail mounts have addressed this issue.
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.
Scopes for ring mounts are available in many different sizes. The most common ones are:
Some less common standards are:
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.[15] One scopes made for ring mounts, it is not uncommon to get ring marks when mounting the rings.
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.[16] A patent was applied for in 1994, and was granted in 1995.[17] Sako Optilock has been sold since some time in the early 2000s.[18] The trade name Optilock was registered in the US in December 1997, and has been marketed in the US since December 2001.[19] In 2000, Sako was sold to Beretta Holding.[20] 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".[17]
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.[21]
Many reflex sights (e.g. red dot sights) and holographic sights have proprietary mounts.[22]
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.[28] 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:
On receivers without an integrated attachment for mounting a scope, for example, an integrated Picatinny rail, the base is usually screwed on as a separate part. Such mounts are often model-specific to the firearm, and depend on factors such as the radius of the receiver bridge, the type of screw and the distance between the screw holes. A common fastening method is by screws. These are often metric M3.5x0.6 mm or US #6–48 (⌀ 3.5 mm, 0.53 mm pitch) or #8–40 (⌀ 4.2 mm, 0.64 mm pitch).
Many European assemblies use M3.5 screws, such as SAKO Optilock, Recknagel and original CZ rings. Since #6–48 and M3.5x0.6 have near identical diameters and almost equal pitch, there is a potential for confusion, and upon mixing the wrong screw will enter the threads, but will gradually become tighter to screw until the thread is destroyed. In case of damage, the hole must often be drilled and re-threaded, and M4x0.7 or #8–40 may then be relevant alternatives.
The Remington 700 Long Action (LA) naturally has a longer distance between the front and rear screw holes, and therefore continuous scope mount assemblies for the 700 LA do not fit on the 700 SA nor the above-mentioned firearms. However, two-piece scope mounts in general interchange for the mentioned models.
In the table below, the radius refers to the curvature of the mounting surface on the receiver bridge. The base is often attached with two screws on the front receiver bridge and two screws on the rear receiver bridge, but sometimes with several more screws. The hole distances are measured from center-to-center. Some common hole distances are 12.7, respectively).[54]
The two front screws are referred to in the list below as screws 1 and 2, and the front hole spacing is thus referred to as «distance 1–2». In the same way, the rear hole distance is called «distance 3–4». The distance between these is largely determined by the receiver length, and is stated here as «distance 2–3»
| Receiver bridge radius (rear, front) | Distance 1–2 (front) | Distance 2–3 (middle) | Distance 3–4 (rear) | Modeller |
|---|---|---|---|---|
| Dovetail, 10.9 mm | 12.7 mm | 76.2 mm | 12.7 mm | Anschütz 64 |
| Dovetail, 11 mm | 22 mm | 80.3 mm | 22 mm | Krieghoff Semprio[55] |
| Dovetail, 11 mm | N/A | N/A | N/A | SIG Sauer SSG 3000,[56] SIG Sauer 200 STR, Accuracy International (several models), CZ 452, CZ 453, CZ 455, CZ 511, CZ 512, CZ 513, Mauser 201, Keppeler (several models) |
| Dovetail, 11.26 mm | 12.7 mm | 76.2 mm | 12.7 mm | Anschütz 54[57] |
| Dovetail, 16.5 mm | 21.84 mm |
| 21.84 mm | Tikka T3 (*82.2 mm), 55, 65, 558, 590, 690, Tikka Master, Tikka T1 (*63.8 mm). |
| Dovetail, 19.5 mm | N/A | N/A | N/A | CZ 527 Standard, 550 Standard, 550 Magnum[58] |
| 14 mm, 16.5 mm | 21.84 mm | 95.8 mm | 12.74 mm | Carl Gustaf 1900, Husqvarna 1900, Antonio Zoli 1900 |
| 12 mm, 24 mm | 21.84 mm | 88.5 mm | 15.4 mm | Merkel SR1 |
| 15 mm | 12.5 mm | 73.5 mm | 12.5 mm | Schultz & Larsen Legacy[59] |
| 15 mm | 21.84 mm | 22.10 mm | 21.84 mm | Anschütz 1727. Distance 1–2: 21.84 mm; distance 2–3: 22.10 mm; distance 3–4: 21.84 mm; distance 4–5: 58.67 mm; distance 5–6: 21.84 mm. |
| 15 mm | 35 mm | 35 mm | N/A | Anschütz 1827 Fortner |
| 15.65 mm | 21.84 mm | 52.3 mm | 15.4 mm | Remington Model 4, 6, 750, Remington 870 (12 and 20 gauge), 870 TAC, 7400, 7600, Benelli M1, M1 Super 90, M2, M3.
|
| 15.9 mm | 22 mm | 102.4 mm | Varies,0–13.2 mm | Mauser K98 Mauser large ring: Modell 98, Centaurian, FN, Interarms Mark X, Parker Hale 1200, Santa Barbara, as well as Mexican Mausers. |
| 16.5 mm | 22 mm | 88.4 mm | 22 mm | Carl Gustaf 3000, Sauer 80, 90, 92 |
| 16.5 mm, 15 mm | 22 mm | 103.4 mm | 12.7 mm | Krico Model 700, 900, 902 |
| 16.5 mm | 22 mm | 107.4 mm | 22 mm | Carl Gustaf 2000 |
| 16.5 mm, 18 mm | 21.9 mm | 110.9 mm | 12.8 mm | Heym SR21 |
| 16.5 mm, 15 mm | 21.9 mm | 118.5 mm | 12.8 mm | Heym SR30 |
| (missing) | 21.84 mm | 101.66 mm | 12.8 mm | Mauser M12 (not the same as Sauer 101) |
| (missing) | 12.8 mm | 54 mm | 12.8 mm | Mossberg 500, 535, 835 |
| 17 mm | 21.84 mm | 98.0 mm | 21.84 mm | Schultz & Larsen Classic DL, 68 DL, 84, 97 DL, 97, M97 |
| 17 mm | 21.84 mm | 110 mm | 21.84 mm | Rößler Titan 3, Titan 6, Titan α |
| 17 mm | 21.84 mm | 101.0 mm | 21.84 mm | Schultz & Larsen Ambassador, Victory[60] |
| 17 mm / * | 21.84 mm | 100.1 mm | 21.84 mm | Savage (short action): Savage Axis, Savage Edge, Roessler Titan.
|
| 17 mm / * | 21.84 mm | 117.58 mm | 21.84 mm | Savage (long action)*Newer models have a radius on both the front and rear receiver bridges, while older models have a radius on the front bridge and a flat on the rear bridge. |
| 17 mm, 34 mm | 21.84 mm | 81.7 mm | 12.7 mm | Winchester Model 70 (WSSM) |
| 17 mm, 34 mm | 21.84 mm | 82.8 mm | 21.84 mm | Winchester Model 70 (short action) |
| 17 mm, 34 mm | 21.84 mm | 85.1 mm | 21.84 mm | Winchester XPR Short |
| 17 mm, 34 mm | 21.84 mm | 89.4 mm | 21.84 mm | Winchester Model 70 (WSM) |
| 17 mm, 34 mm | 21.84 mm | 96.5 mm | 21.84 mm | Winchester Model 70 (long action) |
| 17 mm, 34 mm | 21.84 mm | 98.1 mm | 21.84 mm | Winchester XPR Long |
| 17 mm, 34 mm | 21.84 mm | 109.5 mm | 21.84 mm | Winchester Model 70 (X-Long) |
| 17 mm, 51 mm | 21.84 mm | 82.4 mm | 21.84 mm | Remington 783 Short |
| 17 mm, 51 mm | 21.84 mm | 90 mm | 21.84 mm | Remington 783 Long |
| 17 mm, 51 mm | 21.84 mm | 92.2 mm | N/A | Remington Model 600, 660, Mohawk |
| 17 mm, 51 mm | 21.84 mm | 113.9 mm | 15.4 mm | Haenel Jäger 10 |
| 17 mm, 51 mm | 21.84 mm | 114 mm | 15.35 mm | Rößler Titan 16 |
| 17 mm, 60 mm | 21.8 mm | (missing) | 15.4 mm | Howa 1500 (mini action) |
| 17 mm, 60 mm | 21.84 mm | 87 mm | 15.4 mm | Sabatti Rover 600 (short action) |
| 17 mm, 60 mm | 21.84 mm | 98.5 mm | 15.4 mm | Howa 1500 (short action) |
| 17 mm, 60 mm | 21.84 mm | 102.7 mm | 15.4 mm | Sabatti Rover 780 (long action) |
| 17 mm, 60 mm | 21.84 mm | (missing) | 15.4 mm | Weatherby 300 |
| 17 mm, 60 mm | 21.84 mm | (missing) | 15.4 mm | Weatherby Europa |
| 17 mm, 60 mm | 21.84 mm | 98.5 mm | 15.4 mm | Weatherby Vanguard Short |
| 17 mm, 60 mm | 21.84 mm | 113 mm | 15.4 mm | Weatherby Vanguard Long, Mark V Short |
| 17 mm, 60 mm | 21.84 mm | 114 mm | 15.4 mm | Howa 1500 (long action) |
| 17.2 mm, 50.8 mm | 21.84 mm | 92.2 mm | 15.4 mm | Remington 700-kortkasse (short action, SA). Also used on Remington Model 722, 40x, 78, 740, 742, 760, 710, 721, 722 and 725, Mauser M96 / 96S and SR 97, Sauer 100, Sauer 101, Mauser M18 (not M12), Roessler Titan 16, Bergara B14 LA, Haenel Jäger 10, Sabatti Rover LA. |
| 17.2 mm, 50.8 mm | 21.84 mm | 113.9 mm | 15.4 mm | Remington 700-langkasse (long action, LA). Sauer 100, Sauer 101. |
| 17.4 mm | 21.8 mm | 93 mm | 21.8 mm | Sauer 200 (not 200 STR) |
| 17.4 mm | 21.84 mm | 94.2 mm | 21.84 mm | Sauer 202 |
| 17.4 mm | 21.84 mm | 100.2 mm | 21.84 mm | Sauer 202 Magnum |
| 17.5 mm | 21.9 mm | 98.5 mm | 2x15.4 mm | Anschütz 1780,[61] 1781 |
| 17.5 mm | 21.84 mm | 98.5 mm | 2X15.4 mm | Haenel SLB 2000 Plus (+), H&K SLB 2000 |
| 17.5 mm | 21.84 mm | 98.5 mm | 2x15.4 mm | Merkel SR1 Basic |
| 17.5 mm | 10 mm | 99.9 mm | 10 mm | Steyr-Mannlicher Luxus (l, m, s) |
| 17.5 mm | 10 mm | 100.5 mm | 10 mm | Steyr-Mannlicher (medium action, older models) |
| 17.5 mm | 21.84 mm | 56 mm | 21.84 mm | Steyr-Mannlicher (super short action): Classic, Pro Hunter |
| 17.5 mm | 21.84 mm | 76 mm | 21.84 mm | Steyr-Mannlicher (short action): Classic, Pro Hunter, Export, SM12 |
| 17.5 mm | 21.84 mm | 83 mm | 21.84 mm | Steyr-Mannlicher (medium action): Classic, Pro Hunter, Export, SM12 |
| 17.5 mm | 21.84 mm | 87.5 mm | 21.84 mm | Steyr-Mannlicher (long action): Classic, Pro Hunter, Export, SM12 |
| 17.5 mm, 18 mm, 14 mm | (varies) | (varies) | (varies) | Mauser Modell 93, 94, 95 and 96, samt Kurz. Mauser small ring (G33/40, vz. 33). |
| 18 mm | 12.7 mm | 81 mm | 12.7 mm | Browning Acera, Browning Maral, Benelli ARGO, Browning BAR, Winchester SXR Vulcan, Fabarm Iris |
| 19.1 mm | (varies) | (varies) | (varies) | Mauser Magnum (commercial) |
| 34 mm | 21.8 mm | 82.4 mm | 21.8 mm | Sako A7 (short action) |
| 34 mm | 21.8 mm | 84.5 mm | 21.8 mm | Sako A7 (medium action) |
| 34 mm | 21.8 mm | 95.5 mm | 21.8 mm | Sako A7 (long action) |
| 34 mm (35.6 mm) | 21.84 mm | 76 mm | 14 mm | Browning A-Bolt (short I) |
| 34 mm (35.6 mm) | 21.8 mm | 79 mm | 21.8 mm | Browning A-Bolt (short II) |
| 34 mm (35.6 mm) | 21.8 mm | 82.5 mm | 21.8 mm | Browning A-Bolt (short III) |
| 34 mm (35.6 mm) | 21.8 mm | 98.1 mm | 21.8 mm | Browning A-Bolt (long III) |
| (missing) | 17.78 mm | 71.74 mm | 17.78 mm | Browning X-Bolt (super short) |
| (missing) | 17.78 mm | 74.74 mm | 17.78 mm | Browning X-Bolt (short) |
| (missing) | 17.78 mm | 93.84 mm | 17.78 mm | Browning X-Bolt (long) |
| 38.1 mm | 12.7 mm | 65.35 mm | 15.4 mm | Ruger 10/22 |
| Flat | 12.7 mm | 47.6 mm | 12.7 mm | Marlin 1894 |
| Flat | 12.7 mm | Varies* | 12.7 mm | Marlin Model 1894, 1895, 336, 338, 308, 444.*The distance between the front and rear base varies, and can for instance be 47.6 mm, 60.3 mm or 69.85 mm. |
Quick release (QR) can refer to several different variants of scope mounts which can be mounted and disassembled quickly without tools.
In some cases, it may be relevant to add extra inclination to the scope to be able to shoot at longer (or shorter) distance. For example, this is popular for long range shooting, where it is common to use a tilt of 6 mrad (20 MOA). Extra tilt can be achieved several ways, like for example with a tilted Picatiny rail (e.g. 6 mrad tilt), with bases or rings (e.g. 6 mrad tilt) or with special insert rings (e.g. Burris Pos-Align).[62]
The height of scope sight can be important for the cheek rest support (often called cheek weld) to gain correct eye placement, as well as for calculating ballistics (e.g. a ballistic table). The latter is particularly relevant at very close ranges (e.g. 15m (49feet)), while at longer distances, such as in long range shooting, the scope height has less impact on the ballistic calculations.
The height of a scope sight can be measured in many ways. With regard to ballistic calculations, it is generally only measured from the center of the bore axis to the center of the scope sight (sightline). With regard to cheek support, several methods are used: On firearms with a picatinny rail, the height is measured from the top of the picatinny rail on the firearm. On most other types of bases it is common to measure from the top radius of the receiver bridge.
When the bottom measuring point is determined, the height is then measured up to either the optical center or the bottom of the scope tube, on scopes for ring mounts. The difference between these two measuring methods is distance from the optical center to the bottom of the scope tube, and usually corresponds to half of the tube diameter (e.g. 15 mm on binoculars with a 30 mm tube).