WINDAGE is the quantity by which the bore of a gun, mortar, or howitzer exceeds that of the shot or shell which is to be discharged from it.
The deviations of shot and shells from a truly spherical figure, and the inequalities in the bore of the ordnance, were formerly consider. able ; and on these amounts it was necessary to have a sufficient difference between the presumed diameters of the ball and bore, in order to ensure the possibility of making the former enter into the latter : it followed, from the greatness of this difference, which in the British service was about one-twentieth of the diameter of the bore, that much of the fired gunpowder escaped without producing any impulse 011 the shot, and that the latter was driven from one part of the surface of the bore to another; so that, on being expelled from the gun, it deviated widely from the intended direction of its flight.
From the year 1775, when Dr. Hutton made his first experiments on the velocities of shot, the disadvantage attending a great windage was kuowu, and a diminution of its quantity was proposed ; but the precise amount of the force lost by it was not ascertained till the years 1781 and 17S6, when experiments were made for the purpose, in part, of determining that important circumstance. From these it appeared
that about one-fifth of the charge of powder was last by a windage equal to '06 inch, or of the calibre (=2 inches), and a further loss, amounting to between ith and of the charge, was occasioned by an increase equal to of an inch above the former windage.
The correct geometrical forms which are now given to the balls, and also to the bores, permit the windage to bo reduced much below its former value ; it now varies only from Ath to And of the calbre, in ro case exceeding inch even for the largest guns, and is still in procoss of reduction, as the manufacture of shot and shells advances in precision.