Iron sights
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Iron sights are a system of physical alignment markers (usually made of
Iron sights are typically composed of two components mounted perpendicularly above the weapon's
The earliest and simplest iron sights were fixed and could not be easily readjusted. Many modern iron sights are designed to be adjustable for sighting in firearms by adjusting the sights for elevation or windage.[2] On many firearms it is the rear sight that is adjustable.
For precision shooting applications such as
Principles
In the case of firearms, where the projectile follows a curved ballistic trajectory below the bore axis, the only way to ensure it will hit an intended target is by aiming at the precise point on the trajectory at that target's intended distance. To do that, the shooter aligns their line of sight with the front and rear sights, forming a consistent line of aim (known as the sight axis) and in turn producing what is known as the point of aim (POA) within their own field of view, which then gets pointed directly (i.e. aimed) at the target. The physical distance between the front and rear sights is known as the sight radius, the longer of which produces smaller angular errors when aiming.
"
Rear sights on
In the case of handguns, the rear sight will be mounted on the frame (for revolvers, derringers, and single-shots) or on the slide (for semi-automatic pistols). Exceptions are possible depending on the type of handgun, e.g. the rear sight on a snub-nose revolver is typically a trench milled into the top strap of the frame, and the front sight is the to-be-expected blade. Certain handguns may have the rear sight mounted on a hoop-like bracket that straddles the slide.
With typical blade- or post-type iron sights, the shooter would center the front sight's post in the notch of the rear sight and the tops of both sights should be level.
Due to
Sights for shotguns used for shooting small, moving targets (such as skeet shooting, trap shooting, and clay pigeon shooting) work quite differently. The rear sight is completely discarded, and the rear reference point is provided by the correct and consistent positioning of the shooter's head. A brightly colored (generally the bead is made of a polished metal such as brass and silver, or a plastic fluorescent material, such as green and orange) round bead is placed at the end of the barrel. Often, this bead will be placed along a raised, flat rib, which is usually ventilated to keep it cool and reduce mirage effects from a hot barrel. Rather than being aimed like a rifle or handgun, the shotgun is pointed with the focus always on the target, and the unfocused image of the barrel and bead are placed below the target (the amount below depends on whether the target is rising or falling) and slightly ahead of the target if there is lateral movement. This method of aiming is not as precise as that of a front sight/rear sight combination, but it is much faster, and the wide spread of shots can allow an effective hit even if there is some aiming error. Some shotguns also provide a mid-bead, which is a smaller bead located halfway down the rib, which allows more feedback on barrel alignment. Some shotguns may also come equipped with rifle-style sights. These types of sights are typically found on shotguns intended for turkey hunting.
Types
Open sights
Open sights generally are used where the rear sight is at significant distance from the shooter's eye. They provide minimum occlusion of the shooter's view, but at the expense of precision. Open sights generally use either a square post or a bead on a post for a front sight. To use the sight, the post or bead is positioned both vertically and horizontally in the center of the rear sight notch. For a center hold, the front sight is positioned on the center of the target, bisecting the target vertically and horizontally. For a 6 o'clock hold, the front sight is positioned just below the target and centered horizontally. A 6 o'clock hold is only good for a known target size at a known distance and will not hold zero without user adjustment if these factors are varied.[4] From the shooter's point of view, there should be a noticeable space between each side of the front sight and the edges of the notch; the spaces are called light bars, and the brightness of the light bars provides the shooter feedback as to the alignment of the post in the notch. Vertical alignment is done by lining up the top of the front post with the top of the rear sight, or by placing the bead just above the bottom of the V or U-notch. If the post is not centered in the V or U notch, the shot will not be accurate. If the post extends over the V or U-notch it will result in a high shot. If the post does not reach the top of the V or U-notch it will result in a low shot.
Patridge sights, named after inventor E. E. Patridge, a 19th-century American sportsman, consist of a square or rectangular post and a flat-bottomed square notch and are the most common form of open sights, being preferred for target shooting, as the majority of shooters find the vertical alignment is more precise than other open sights. V-notch and U-notch sights are a variant of the patridge which substitute a V- or U-shaped rear notch.[2]
Other common open sight types include the buckhorn, semi-buckhorn, and express. Buckhorn sights have extensions protruding from either side of the rear sight forming a large ring which almost meets directly above the "V" of the notch. The semi-buckhorn is similar but has a wider gently curving notch with the more precise "V" at its center and is standard on classic
Open sights have many advantages: they are very common, inexpensive to produce, uncomplicated to use, sturdy, lightweight, resistant to severe environmental conditions, and they do not require batteries. On the other hand, they are not as precise as other forms of sights, and are difficult or impossible to adjust. Open sights also take much more time to use—the buckhorn type is the slowest, patridge, "U" and "V" type notch sights are only a bit quicker; only the express sight is relatively fast. In addition, open sights tend to block out the lower portion of the shooter's field of view by nature, and because of the depth of field limitations of the human eye, do not work as well for shooters with less than perfect vision.[2]
Shotgun sights
Among those utilizing
In the tactical environment, where targets aren't moving across the visual field as quickly, sights do have a role. For many, a
Many shotgun bead sights are designed for a "figure 8" configuration, where a proper sight picture uses a bead mounted at the midpoint of the barrel in conjunction with a front bead mounted toward the muzzle. Many shotgun manufacturers, such as Browning, calibrate these sighting systems to produce a shotgun pattern that is "dead-on" when the front bead is stacked just above the mid-bead, producing the figure-8 sight picture.[9]
Aperture sights
Aperture sights, also known as "peep sights", range from the "ghost ring" sight, whose thin ring blurs to near invisibility (hence "ghost"), to target aperture sights that use large disks or other occluders with pinhole-sized apertures. In general, the thicker the ring, the more precise the sight, and the thinner the ring, the faster the sight.[2][additional citation(s) needed]
The theory of operation behind the aperture sight is often stated that the human eye will automatically center the front sight when looking through the rear aperture, thus ensuring accuracy.[2][additional citation(s) needed] However, aperture sights are accurate even if the front sight is not centered in the rear aperture due to a phenomenon called parallax suppression.[10][additional citation(s) needed] This is because, when the aperture is smaller than the eye's pupil diameter, the aperture itself becomes the entrance pupil for the entire optical system of target, front sight post, rear aperture, and eye. As long as the aperture's diameter is completely contained within the eye's pupil diameter, the exact visual location of the front sight post within the rear aperture ring does not affect the accuracy, and accuracy only starts to degrade slightly due to parallax shift as the aperture's diameter begins to encroach on the outside of the eye's pupil diameter. An additional benefit to aperture sights is that smaller apertures provide greater depth of field, making the target less blurry when focusing on the front sight.
In low light conditions the parallax suppression phenomenon is markedly better. The depth of field looking through the sight remains the same as in bright conditions.[10] This is in contrast to open sights, where the eye's pupil will become wider in low light conditions, meaning a larger aperture and a blurrier target. The downside to this is that the image through an aperture sight is darker than with an open sight.
These sights are used on target rifles of several disciplines and on several military rifles such as the Pattern 1914 Enfield and M1917 Enfield, M1 Garand, the No. 4 series Lee–Enfields, M14 rifle, Stgw 57, G3 and the M16 series of weapons along with several others. Rifle aperture sights for military combat or hunting arms are not designed for maximal attainable precision like target aperture sights, as these must be usable under suboptimal field conditions.[11]
Ghost ring
The ghost ring sight is considered by some to be the fastest type of aperture sight.[neutrality is disputed] It is fairly accurate, easy to use, and obscures the target less than nearly all other non-optical sights. Because of this, ghost ring sights are commonly installed on riot and combat shotguns and customized handguns, and they are also gaining ground as a backup sighting system on rifles.[citation needed] The ghost ring is a fairly recent innovation, and differs from traditional aperture sights in the extreme thinness of the rear ring and the slightly thicker front sight. The thin ring minimizes the occlusion of the target, while the thicker front post makes it easy to find quickly. Factory Mossberg ghost ring sights also have thick steel plates on either side of the extremely thin ring. These are to protect the sight's integrity in cases where, if the shotgun were to fall and impact a surface in a way that could potentially damage or distort the shape of the ring.
Target aperture sights
Target aperture sights are designed for maximum precision.[12] The rear sight element (often called "diopter") is usually a large disk (up to 1 inch or 2.5 cm in diameter) with a small hole in the middle, of approximately 1.2 mm (0.047 in) or less, and is placed close to the shooter's eye.[13] High end target diopters normally accept accessories like adjustable diopter aperture and optical filter systems to ensure optimal sighting conditions for match shooters. Typical modern target shooting diopters offer windage and elevation corrections in 2 mm (0.079 in) to 4 mm (0.157 in) increments at 100 m (109.4 yd). Some International Shooting Sport Federation (ISSF) (Olympic) shooting events require this precision level for sighting lines, since the final score of the top competitors last shots series is expressed in tenths of scoring ring points.
The complementing front sight element may be a simple bead or post, but is more often a "
The use of round rear and front sighting elements for aiming at round targets, like used in ISSF match shooting, takes advantage of the natural ability of the eye and brain to easily align
Front aperture size selection
Front aperture size is a compromise between a tight enough aperture to clearly define the aiming point and a loose enough aperture so as to not cause 'flicker'. When the aperture is too small, the boundary between the target and front aperture outline becomes indistinct, requiring the shooter to consciously or subconsciously generate small eye movements to measure the distance around the target. USA Shooting recommends a front aperture that creates at least 3 Minutes of Angle (MOA) of boundary space. In research performed by Precision Shooting, it was found that this increased shooter confidence, reduced hold times, and created more decisive shots.[14] There may be an upper bound to the front aperture size that improves performance, however. In 2013, researchers performed experiments with the game of golf, specifically the skill of putting which is another skill that combines visual alignment with motor skills. They found that by manipulating the perceived size of the target (the golf hole) by surrounding it with concentric rings of various sizes, there was a phenomenon that improved performance when the target was surrounded by smaller circles thereby increasing its perceived size. They found that when the target was perceived as larger, performance increased.[15]
Non-target aperture sights
Aperture sights on military rifles use a larger aperture with a thinner ring, and generally a simple post front sight.
Rifles from the late 19th century often featured one of two types of aperture sight called a "
Flip up sights
Adjustment
Fixed sights are sights that are not adjustable. For instance, on many
The downside to adjustable sights is the inherent fragility of the moving parts. A fixed sight is a solid piece of metal, usually steel, and if firmly attached to the gun, little is going to be able to damage it beyond usefulness. Adjustable sights, on the other hand, are bulkier, and have parts that must move relative to the gun. Solid impact on an adjustable sight will usually knock it out of adjustment, if not knock it right off the gun. Because of this, guns for self defense or military use either have fixed sights, or sights with "wings" on the sides for protection (such as those on the M4 carbine).
Iron sights used for hunting guns tend to be a compromise. They will be adjustable, but only with tools—generally either a small
The most common is a rear sight that adjusts in both directions, though military rifles often have a tangent sight in the rear, which a slider on the rear sight has pre-calibrated elevation adjustments for different ranges. With tangent sights, the rear sight is often used to adjust the elevation, and the front the windage. The M16A2 later M16 series rifles have a dial adjustable range calibrated rear sight, and use an elevation adjustable front sight to "zero" the rifle at a given range. The rear sight is used for windage adjustment and to change the zero range.
Enhancements
While iron sights are very simple, that simplicity also leads to a staggering variety of different implementations. In addition to the purely geometric considerations of the front blade and rear notch, there are some factors that need to be considered when choosing a set of iron sights for a particular purpose.
Glare reduction
Glare, particularly from the front sight, can be a significant problem with iron sights. The glare from the front sight can increase the apparent brightness of the light bar on one side of the sight, causing windage errors in aiming, or lower the apparent height of the front sight, causing elevation errors in aiming. Since the direction of the ambient light is rarely constant for a shooter, the resulting changing glare can significantly affect the point of aim.
The most common solution to the problem of glare is a matte finish on the sights. Serrating or bead blasting the sight is a common solution for brightly finished sights, such as blued steel or stainless steel. Matte finishes such as
Many target sights are designed with vertical or even undercut front sight blades, which reduces the angles at which light will produce glare off the sight—the downside of these sights is that they tend to snag on clothing, branches, and other materials, so they are common only on target guns. Sight hoods reduce the chances of snagging an undercut sight and are common on some types of rifles, particularly
Contrast enhancements
While target shooters generally prefer a
- Three-dot
- On semi-automatic handguns, the most common type of enhancement is a bright white dot painted on the front sight near the top of the blade, and a dot on each side of the rear sight notch. In low lighting conditions the front sight dot is centered horizontally between the rear sight dots, with the target placed above the middle (front) dot. Some sight vendors offer differently colored dots for the front and rear sights.[16]
- White outline rear
- A contrast variation which uses a dot front sight with a thick and bright white outline around the rear sight notch.[17]
- Straight Eight
- Heinie Specialty Products produces a variant of high visibility sights in which a single dot front sight and a rear notch with a dot below can be lined up vertically to form a figure "eight".[18]
- Sight inserts
- Popular on revolvers, this enhancement consists of a colored plastic insert in the front sight blade, usually red or orange in color.[19]
- Bar / dot or express sight
- Similar to the Straight Eight type, this type of sight is traditional on express rifles and is also found on some handguns. The open, V-shaped rear allows for faster acquisition and wider field of view, though less accurate for longer range precision type shooting. The dot on the front sight is aligned or set directly above the vertical bar on the rear sight, commonly referred to as "dotting the 'I'".[16]
- Gold bead
- Preferred by many competitors in IPSC and IDPA shooting.[16]
- Night sights
- On tactical firearms, the contrast enhancements can consist of small fiber opticsights with tritium vials to provide bright, high-contrast firearms sights in both bright and dim conditions.
- Fiber optic
- A growing trend, started on air rifles and muzzleloaders, is the use of short pieces of optical fiber for the dots, made in such a way that ambient light falling on the length of the fiber is concentrated at the tip, making the dots slightly brighter than the surroundings. This method is most commonly used in front sights, but many makers offer sights that use fiber optics on front and rear sights. Fiber optic sights can now be found on handguns, rifles, and shotguns, both as aftermarket accessories and a growing number of factory guns.[21]
See also
Notes
- ^ Calculations assume a 660 mm (26 in) sight radius or sighting line
References
- ^ merriam-webster.com - iron sight a metallic sight for a gun as distinguished from a sight depending on an optical or computing system[permanent dead link]
- ^ a b c d e f g h i Hawks, Chuck. "Choosing the Right Sight", Chuck Hawks Web site. Retrieved July 24, 2008.
- ^ Hacker, Rick (2010-09-23). "Peep Show". RifleShooter. Guns & Ammo Network. Retrieved 18 July 2017.
- ^ "CMP - First Shot Online!". www.odcmp.org.
- ^ "Shooting a Shotgun vs. a Rifle | OR | Hunter Ed.com™". www.hunter-ed.com. Retrieved 2018-04-22.
- ^ "Clays Shooting: Tips from the Shotgun Pros". Range365. Archived from the original on 2021-03-08. Retrieved 2018-04-22.
- ^ "Why Shotguns and Fiber-Optics Don't Mix". www.outdoorlife.com. Archived from the original on 2017-09-26. Retrieved 2018-04-22.
- ^ "Sighting Systems for the Defensive Shotgun - Lucky Gunner Lounge". www.luckygunner.com. Retrieved 2018-04-22.
- ^ "Point of Impact". www.browning.com. Retrieved 2018-04-22.
- ^ a b Burdge, Robert J.; Kerr, Douglas A. "Parallax Suppression with a Target Rifle Aperture Sight" (PDF). Retrieved 6 February 2015.
- ^ "The Ultimate Guide to the AR15 Iron Sights Ver 1.1". 16 May 2016. Retrieved 2022-02-04.
- ^ Head Position, Diopter Interval and Lint by Heinz Reinkemeier, UIT Journal at www.issf-sports.org
- ^ "Use of sight and choosing sight insert (Norwegian: Bruk av sikte og valg av hullkorn) - From an article published in the Norwegian newsletter Norsk Skyttertidende by John Olav Ågotnes" (PDF). Archived from the original (PDF) on 2017-10-30. Retrieved 2018-10-17.
- ^ O'Connor, J.P. (January 3, 2011). "Where Are You Looking?" (PDF). USA Shooting. Archived from the original (PDF) on March 8, 2021. Retrieved April 22, 2018.
- S2CID 1671695.
- ^ a b c "Description Of Sights" Novak Sights Web site. Retrieved July 29, 2008.
- ^ "Sight Accessories - .126 White Outline Rear Sight Blade Kit" Archived 2009-03-03 at the Wayback Machine Smith & Wesson Web site. Retrieved July 29, 2008.
- ^ "Heinie Straight Eight Sights" Archived 2009-03-01 at the Wayback Machine Heinie Specialty products Web site. Retrieved July 29, 2008.
- ^ "Handgun Sights" Archived 2009-03-05 at the Wayback Machine Kimber of America Web site. Retrieved July 29, 2008.
- ^ Hawks, Chuck. "AmeriGlo Independent Light Tritium Night Sights", Chuck Hawks Web site. Retrieved July 29, 2008.
- ^ "Novak Fiber Optic Sights" Novak Sights Web site. Retrieved July 29, 2008.