Page:Miscellaneous Papers on Mechanical Subjects.djvu/95

 difference existed between the two shapes, for in other respects the flat-fronted projectile has many advantages. Besides being the form best adapted, as has been said, for firing against iron plates, it may be used for penetrating through water; in this respect I have succeeded in obtaining results which, while they are most important, were, I believe, previously considered unattainable. For firing through elastic materials, tubular projectiles, as shown in fig. D are used. They are fired with a wooden wad, and take out a core from the object perforated, leaving a corresponding hole which does not close up. The tubular projectiles also penetrate deeper into masonry than those of any other shape I am acquainted with.

The system of rifling which has been described with reference more particularly to small arms, is equally applicable to ordnance of all sizes. The principle of construction is simple and the extent of bearing afforded by the rifling surfaces provides amply for the wear of the interior of the gun; any requisite allowance for windage may be made at the same time that the projectile is kept concentric with the bore. When it enters the gun it bears upon a certain portion of each side of the hexagon, and when it comes out it bears on the opposite portion,—by easing off, therefore, that half of