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

In particular he carried out an extensive series of experiments in gunnery, embodying his results in his famous treatise on ' New Principles in Gunnery' (1742), which contains a description of his ballistic pendulum (see gun chronograph).

To ensure accurate results, immediately prior to use, the gelatin block is "calibrated" by firing into it a standard .177 caliber (4.5 mm) steel BB, from an air gun over a gun chronograph into the gelatin, and the depth of penetration measured.