page_title: Iron sights
section_title: Open sights
hierarchical_section_title: Iron sights / Open sights
context_page_description: Iron sights are a system of shaped alignment markers used as a sighting device to assist in the aiming of a device such as a firearm, crossbow, or telescope, and exclude the use of optics as in reflector sights, holographic sights, and telescopic sights.
  Iron sights are typically composed of two component sights, formed by metal blades: a rear sight mounted perpendicular to the line of sight and a front sight that is a post, bead, ramp, or ring. Open sights use a notch of some sort as the rear sight, while aperture sights use some form of a circular hole. Civilian, hunting, and police firearms usually feature open sights, while many military battle rifles employ aperture sights.
  The earliest and simplest iron sights are fixed and cannot be easily adjusted. Many iron sights are designed to be adjustable for sighting in firearms by adjusting the sights for elevation or windage. On many firearms it is the rear sight that is adjustable.
  For precision applications such as hunting or sniping, the iron sights are usually replaced by a telescopic sight. Iron sights may still be fitted alongside other sighting devices for back-up usage.
context_section_description: 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. 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.
  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 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. These sights do not occlude the target as much as some other styles which is useful in the case of a charging animal.  In cases where the range is close and speed far outweighs accuracy (e.g. the shooter is being charged by dangerous big-game), the front sight is used like a shotgun bead; the rear sight is ignored, and the bead is placed on the target. When more time is available, the bead is placed in the "V" of the rear sight.
  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.
caption: A selection of open sights, and one aperture sight suitable for use with long eye relief: A) U-notch and post, B) Patridge, C) V-notch and post, D) Express, E) U-notch and bead, F) V-notch and bead, G) trapezoid, H) ghost ring. The gray dot represents the target