A ballistic chronograph or gun chronograph is a

measuring instrument Instrumentation is a collective term for measuring instruments, used for indicating, measuring, and recording physical quantities. It is also a field of study about the art and science about making measurement instruments, involving the related ...

used to measure the

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

of a

projectile A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found ...

flight Flight or flying is the motion (physics), motion of an Physical object, object through an atmosphere, or through the vacuum of Outer space, space, without contacting any planetary surface. This can be achieved by generating aerodynamic lift ass ...

, typically fired from a

gun A gun is a device that Propulsion, propels a projectile using pressure or explosive force. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns or water cannon, cannons), or gas (e.g. light-gas gun). So ...

or other

firearm A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions). The first firearms originate ...

. The instrument is often useful for tasks such as gauging the utility of a

or safety of less-lethal projectiles fired from items such as a paintball gun or

BB gun A BB gun is a type of air gun designed to shoot metallic spherical projectiles called BBs (not to be confused with similar-looking bearing balls), which are approximately the same size as BB-size lead birdshot used in shotguns ( in diameter) ...

History

Benjamin Robins (1707–1751) invented the ballistic pendulum that measures the

momentum In Newtonian mechanics, momentum (: momenta or momentums; more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. ...

of the

fired by a

. Dividing the momentum by the projectile

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

gives the

. Robbins published his results as ''New Principles of Gunnery'' in 1742. The ballistic pendulum could make only one measurement per firing because the device catches the projectile. The gun's accuracy also limited how far down range a measurement could be made. Alessandro Vittorio Papacino d'Antoni published results in 1765 using a wheel chronometer. This used a horizontal spinning wheel with a vertical paper mounted on the rim. The bullet was fired across the diameter of the wheel so that it pierced the paper on both sides, and the angular difference along with the rotation speed of the wheel was used to compute the bullet velocity. 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. 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 Woolwich () is a town in South London, southeast London, England, within the Royal Borough of Greenwich. The district's location on the River Thames led to its status as an important naval, military and industrial area; a role that was mainta ...

, 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. The first electronic ballistic chronograph was invented by Kiryako ("Jerry") Arvanetakis in the 1950s. As consulting engineer under contract by NACA (later

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

), 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 crewed space flight. His first design was an open rectangular frame of square

aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

tubing with a screen of fine copper wire at both ends. Breaking the first wire started charging a

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

, breaking the second wire stopped it. Measuring the accumulated voltage and knowing the rate of charge the elapsed time could be accurately calculated.

Modern chronograph

The modern chronograph consists of two sensing areas framed by rods topped by diffusing screens or artificial lighting above (or below) along with optical sensors that detect the passage of the bullet. The time it takes the bullet to travel the distance between the sensors is measured electronically from which velocity is calculated and displayed. Advanced ballistic chronographs include a type employing

Doppler radar A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the fre ...

to measure bullets in free flight at various distances; another is a device mounted at the end of a barrel, which uses magnetic field sensors for the measurement of a bullet's velocity as it exits the muzzle.

References

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History

Modern chronograph

See also

References

Further reading