Gun chronograph

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A Down Range chronograph with storage and statistical tools.

A gun chronograph or shooting chronograph is an instrument used to measure the velocity of a projectile fired by a gun.



Benjamin Robins (1707–1751) invented the ballistic pendulum that measures the momentum of the projectile fired by a gun. Dividing the momentum by the projectile mass gives the velocity. Robbins published his results as New Principles of Gunnery in 1742. [1] [2] The ballistic pendulum could make only one measurement per firing because the device catches the projectile. [3] The gun's accuracy also limited how far down range a measurement could be made. [4]

Benjamin Robins was a pioneering English scientist, Newtonian mathematician, and military engineer.

Ballistic pendulum

A ballistic pendulum is a device for measuring a bullet's momentum, from which it is possible to calculate the velocity and kinetic energy. Ballistic pendulums have been largely rendered obsolete by modern chronographs, which allow direct measurement of the projectile velocity.

Momentum conserved physical quantity related to the motion of a body

In Newtonian mechanics, linear momentum, translational momentum, or simply momentum is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction in three-dimensional space. If m is an object's mass and v is the velocity, then the momentum is

An early chronograph that measures velocity directly was built in 1804 by Grobert, a colonel in the French Army. This used a rapidly rotating axle with two disks mounted on it about 13 feet apart. The bullet was fired parallel to the axle, and the angular displacement of the holes in the two disks, together with the rotational speed of the axle, yielded the bullet velocity. [5]

Grobert is a surname. Notable people with the surname include:

Ingalls (1886 , p. 18) describes Bashforth's chronograph that could make many measurements over long distances:

In 1865 the Rev. Francis Bashforth, M. A., who had then been recently appointed Professor of Applied Mathematics to the advanced class of artillery officers at Woolwich, began a series of experiments for determining the resistance of the air to the motion of both spherical and oblong projectiles, which he continued from time to time until 1880. As the instruments then in use for measuring velocities were incapable of giving the times occupied by a shot in passing over a series of successive equal spaces, he began his labors by inventing and constructing a chronograph to accomplish this object, which was tried late in 1865 in Woolwich Marshes, with ten screens, and with perfect success.

The Bashforth screens were made with several threads and series connected switches. A projectile passing through a screen would break one or more threads, the broken thread caused a switch to momentarily (about 20 ms) interrupt a current as the switch arm moved from its weighted position to its unweighted position, and the momentary interruption would be recorded on a paper chart. [6]

Modern chronograph

The modern chronograph consists of two sensing areas called chronograph screens, which contain optical sensors that detect the passage of the bullet. The bullet is fired so it passes through both screens, and the time it takes the bullet to travel the distance between the screens is measured electronically.

Photodetector sensors of light or other electromagnetic energy

Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. A photo detector has a p–n junction that converts light photons into current. The absorbed photons make electron–hole pairs in the depletion region. Photodiodes and photo transistors are a few examples of photo detectors. Solar cells convert some of the light energy absorbed into electrical energy.

The first electronic ballistic chronograph was invented by Kiryako ("Jerry") Arvanetakis in the 1950s.[ citation needed ] As consulting engineer under contract by NACA (later NASA), he was asked to find a way to accurately measure the velocity of various projectiles fired at hyper-velocities into a variety of engineered materials in anticipation of manned space flight. His first design was an open rectangular frame of square aluminum tubing with a screen of fine copper wire at both ends. Breaking the first wire started charging a capacitor, breaking the second wire stopped it. Measuring the accumulated voltage and knowing the rate of charge the elapsed time could be accurately calculated.

NASA space-related agency of the United States government

The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research.

Capacitor electrical component used to store energy for a short period of time

A capacitor is a passive two-terminal electronic component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. The capacitor was originally known as a condenser or condensator. The original name is still widely used in many languages, but not commonly in English.

See also

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External ballistics Behavior of projectiles in flight

External ballistics or exterior ballistics is the part of ballistics that deals with the behavior of a projectile in flight. The projectile may be powered or un-powered, guided or unguided, spin or fin stabilized, flying through an atmosphere or in the vacuum of space, but most certainly flying under the influence of a gravitational field.

Gun barrel firearm component which guides the projectile during acceleration

A gun barrel is a crucial part of gun-type ranged weapons such as small firearms, artillery pieces and air guns. It is the straight shooting tube, usually made of rigid high-strength metal, through which a contained rapid expansion of high-pressure gas(es) is introduced behind a projectile in order to propel it out of the front end (muzzle) at a high velocity. The hollow interior of the barrel is called the bore. The measurement of the diameter of the bore is called the caliber. Caliber is usually measured in inches or millimetres.

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A gunshot is a single discharge of a gun, typically a man-portable firearm, producing a visible flash, a powerful and loud shockwave and often chemical gunshot residue. The term can also refer to a ballistic wound caused by such a discharge.

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In ballistics, the ballistic coefficient (BC) of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the negative acceleration: a high number indicates a low negative acceleration—the drag on the vehicle or projectile is small in proportion to its mass.

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The Aberdeen chronograph was the first portable gun chronograph, an instrument for measuring the muzzle velocity and striking power of a projectile fired by a gun. It was invented in 1918 by Alfred Lee Loomis at the U.S. Army's Aberdeen Proving Ground.

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Francis Bashforth was a British applied mathematician who studied ballistics.


  1. Ingalls 1886 , p. 17
  2. Robins, Benjamin (1805), New Principles of Gunnery (New ed.), F. Wingrave
  3. Bashforth 1866 , p. 3, "only one observation on each round".
  4. Bashforth 1866 , p. 3, "Beyond 295 feet the gun was not sufficiently accurate".
  5. Prony (1805), "Report of a method of measuring the initial Velocity of Projectiles discharged from Fire-arms, both horizontally and with different Elevations, made to the Physical and Mathematical Class of the National Institute", in Nicholson, William, A Journal of Natural Philosophy, Chemistry and the Arts, XI, London at page 42
    abridged from Journal des Mines No 92 p. 117, May 1804.
  6. Bashforth 1866 , pp. 12–13

Further reading