I have stated that the form of the bore of the Whitworth rifle is polygonal, being a hexagon with rounded edges; it is therefore a combination of a straight line and a circle, and its surfaces are those most easily produced in the workshop.
There is a geometrical simplicity pertaining to the polygonal form which is unattainable by any other form.
The amount of bearing surface for giving rotation, and which also conduces to the centreing of the shot, depends upon the difference between the maximum and minimum diameters of the bore, this difference, in fact, represents the hold which the barrel has upon the projectile. In any grooved system of rifling you pass more rapidly from the maximum to the minimum diameter, and the extent of bearing surface is diminished accordingly, whereas in the hexagonal system, there is a long inclined bearing surface, the section of which is a straight line starting from the minimum diameter and running into a circle at the end of the maximum diameter.
A polygonal rifled projectile is applicable to the largest cannon as well as to small arms, and I have adopted the hexagonal form, because it gives me the best working difference between the maximum and minimum diameters.
It will be observed that the hexagonal form of the projectile is analogous to that of the hexagonal nut universally used.
It may be said that this record of my experiments, showing how the modern rifle has become what it is in range, in penetration, and in accuracy, has ceased to be of interest or importance since the new element of rapid firing has been brought to bear with such important results by the introduction of breech loading. I would state in reply that breech loading and rapid fire give increased importance and value to range, penetration, and accuracy, as the primary and essential qualities of the rifle. However necessary these qualities may have been for the muzzle-loader, they are still more requisite with an arm which must otherwise waste its ammunition. Rapid firing must rest on the very best system of rifling, as its only safe basis.
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