Iron sights

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.

Modern iron sights can all provide some horizontal and vertical adjustments for sighting-in, and often have elevation markings that allow the shooter to quickly compensate (though with rather limited precision) for increasing bullet drops at extended distances.

Rear sights on long guns (such as rifles and carbines) are usually mounted on a dovetail slot on the back part of the barrel or the receiver, closer to the eye of the shooter, allowing for easy visual pick-up of the notch.

[2] 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).

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.

Some shotguns also provide a mid-bead, which is a smaller bead located halfway down the rib, which allows more feedback on barrel alignment.

[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.

V-notch and U-notch sights are a variant of the patridge which substitute a V- or U-shaped rear 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 Winchester and Marlin lever-action rifles.

Express sights are most often used on heavy caliber rifles intended for the hunting of dangerous big game, and are in the form of a wide and large "V" with a heavy white contrast line marking its bottom and a big white or gold bead front sight.

[2] 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.

[6] Because much of shotgunning involves putting a scatter pattern in the path of moving targets, the concept of a sight is considered a subconscious aid.

When shooting, aligning the rear groove with the front bead is not to be consciously considered, as it comprises only a rough reference allowing the shooter to use their natural point of aim to make the shot.

[7] In the tactical environment, where targets aren't moving across the visual field as quickly, sights do have a role.

[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.

[neutrality is disputed] It is fairly accurate, easy to use, and obscures the target less than nearly all other non-optical sights.

The thin ring minimizes the occlusion of the target, while the thicker front post makes it easy to find quickly.

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.

[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.

Tinted transparent plastic insert elements may also be used, with a hole in the middle; these work the same way as an opaque ring, but provide a less obstructed view of the target.

The precise sizes are quite subjective, and depend on both shooter preference and ambient lighting, which is why target rifles come with easily replaceable front sight inserts, and adjustable aperture mechanisms.

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.

Since the black powder used in muzzleloaders and early cartridges was not capable of propelling a bullet at high speed, these sights had very large ranges of vertical adjustments, often on the order of several degrees, allowing very long shots to be made accurately.

The .45-70 cartridge, for example, was tested by the military for accuracy at ranges of up to 1,500 yards (1,372 metres), which required 31⁄3 degrees of elevation.

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.

They generally have large knobs to control horizontal and vertical movement without tools, and often they are designed to be quickly and easily detachable from the gun so they can be stored separately in their own protective case.

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.

Since the direction of the ambient light is rarely constant for a shooter, the resulting changing glare can significantly affect the point of aim.

A variety of different contrast enhancements to the basic Patridge type sight and others have been developed to address this deficiency.