INTERIOR BALLISTICS. In interior ballistics, we calculate the velocity of translation and rota tion which the combustion of a given charge of powder, of known composition and quality, will impart to a given projectile, and the effect upon the gun. Time following definitions will enable the non-technical reader to appreciate better some of the problems with which this science deals: The specific Gravity of powder is the weight of a given volume of powder referred to that of an equal volume of water.
Gravimetric Density is the density of the powder when the spaces between the grains are considered.
Explosion is the rapid conversion of powder into gases and solids with evolution of heat. It may be divided into three parts: Ignition, which is the setting on tire of a part of the grain or charge: Inflammation, which is the spread of the ignition from point to point of the grain or charge; and Combustion, which is the burning of the inflamed grain or charge from the point of ignition.
Velocity of Emission is the rate of evolution of the gas of gunpowder.
A Progressive Powder is one that burns slowly at first and more rapidly afterwards.
Density of Loading is the ratio of weight of the charge of powder to that weight of water, at its maximum density, which will completely fill the volume in which the charge is fired.
The Force of the powder is the pressure per unit of surface exerted by the gases from the unit weight of powder, the gases occupying at the temperature of explosion a volume equal to unity.
The Passive Resistances are those (Inc to the forcing of the band of the projectile into the grooves of the rifling, friction, etc.
The Ballistic Coefficient, `C,' for a given pro jectile depends upon the cross - section and weight of the projectile and the density of the air, and measures the ballistic efficiency of the projectile.
The Factor of Effect is the ratio of the actual work realized by the projectile at the muzzle to the entire work of the charge.
The Energy of the projectile means its power to do work, and is proportional to its weight and the square of its velocity.
titsTom It is only within the last fifty years that the complicated phenomena which take place within the bore of the glum when the charge is fired have been clearly comprehended. The celebrated Benjamin Robins (1740), else where referred to in this article, made many ex periments relating to interior ballistics. His de ductions from his experiments, in spite of the ex tremely erroneous and sometimes absurd opinions on the subject that were entertained in those days, justly entitle Robins to be called the 'father of modern gunnery.' Dr. Hutton's experiments
verify most of Robins's deductions, differing principally in the estimate of maximum tem perature and pressure. D'Arcy (1760) made the first attempt to determine dynamically the law of pressure of gases in the bore of a musket by measuring the velocity of the projectile at different points of the bore. His method was successively to shorten the barrel, and measure, for each length, the velocity of the bullet by means of a ballistic pendulum. From these velocities he got the corresponding accelera tions, and then the pressures by multiplying the accelerations by the mass. Count Rumford (1792) made the first attempt to measure di rectly the pressure of fired gunpowder. The account of his experiments was the most hn portant contribution to interior ballistics which had been made up to that time. His appara tus consisted of a small wrought-iron mortar, mounted, with its axis vertical, upon a solid stone foundation, and having a projecting axial vent with no outside opening. The charge was fired by applying a red-hot ball provided with a hole, into which the projecting vent-tube was inserted, there being no gas lost through the vent by this arrangement. The muzzle was closed by a stopper, upon which rested a weight used for confining the elastic fluid resulting from the combustion of the powder. The charges were increased a grain at a time from 1 grain to 1S grains, and for each charge a weight was found by experiment just sufficient to retain the gaseous product. From the mean of all the observed pressures, Rumford found the maximum pressure—that is, the pressure when the powder entirely tilled the space into which it is fired—to lie 29,178 atmospheres, about four and one-half times the maximum pressure found by Noble and Abel. in an en tirely similar set of experiments, nearly a century later. The result found by Noble and Abel (6554 atmospheres, or 45 tons per square inch) is accepted by all writers on interior bal listics as being very near the truth. Various other scientists did original work of more or less value to the development of interior ballis tics prior to the year 1860. Consult the works of Gay-Lussac, Chevruil, Graham, Cava lli, Mayevski, Otto, Neumann, etc.