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Iron sights are a system of physical alignment markers used as a sighting device to assist the accurate aiming of ranged weapons such as firearms, airguns, crossbows, and bows, or less commonly as a primitive finder sight for optical telescopes. Iron sights, which are typically made of metal, are the earliest and simplest type of sighting device.
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Mark III free gun reflector sight mk 9 variant. Another type of optical sight is the reflector (or "reflex") sight, a generally non-magnifying optical device that allows the user to look through a glass element and see a reflection of an illuminated aiming point or some other image superimposed on the field of view. [7]
Transverse crevasses, Chugach State Park, Alaska. A crevasse is a deep crack that forms in a glacier or ice sheet. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement. The resulting intensity of the shear ...
Crevasse rescue (or crevasse-extraction) is a set of techniques in mountaineering where climbers use their equipment to pull a climber, who has just fallen into a crevasse, to safety. [1] Crevasse rescue is considered a core skill set in alpine climbing, but difficult to do efficiently. [1] [2] It is typically encountered by rope teams on ...
A common form of crevice failure occurs due to stress corrosion cracking, where a crack or cracks develop from the base of the crevice where the stress concentration is greatest. This was the root cause of the fall of the Silver Bridge over the Ohio River , in 1967 in West Virginia , where a single critical crack only about 3 mm long suddenly ...
Telescopic sights have both advantages and disadvantages relative to iron sights. Standard doctrine with iron sights is to focus the eye on the front sight and align it with the resulting blur of the target and the rear sight; most shooters have difficulty doing this, as the eye tends to be drawn to the target, blurring both sights.
The user then adjusts the iron sights or scope reticle to align the point of aim with the projected laser dot. Another more commonly used type of laser boresighter is attached to the muzzle of the barrel, either inserted straight into the bore ("arbor" type) or held in alignment with the barrel via a magnet , and projects a laser beam onto the ...