D extending from the base to the point of the
chamber in a spiral direction. In the drawings, I have shown the pitch
of this spiral as one quarter turn in the length of the chamber, but it
is to be understood that I may use a greater or less pitch without
departing in any way from my invention.

I have shown a pitch of one quarter turn particularly for purposes of
illustration, as if a greater pitch had been used the section Fig. 2
would not have shown any one rib entirely.

As will be seen by Fig. 1, the grain or fiber of the metal is also
twisted spirally in accordance with the pitch of the ribs D, in this
case a quarter turn from the rear end of the projectile to its point.

In order to manufacture a projectile of this character I have devised
the following method which I deem preferable, though I do not wish to
limit myself thereto. This consists first in casting an ingot from
which the solid forging is to be produced. Previous to, during or after
the process of forging, the ingot is twisted in a torsion apparatus,
one end of the ingot being held fixed while the other end is being
rotated by any suitable rotative gripping mechanism through an arc of
the number of degrees desired. This will result in what I term a "twist
forging" in which the grain or fiber will lie in any predetermined or
desired spiral direction or pitch. The spiral ribs which are to lie in
the direction preferably parallel to the grain or fiber of the metal
may now be formed by the boring process similar to that employed in the
rifling of modern artillery.

My projectile might also be formed by forming the shell with the ribs
running longitudinally there along in a direct line from front to rear
and with the fiber of the metal also running in a direct line parallel
with the ribs. The projectile might then be reheated for forging and
while being forged the rear could be held in any suitable gripping
device and the forward end be rotated, as before explained. Thus the
fiber of the shell and the interior ribs will both be given the spiral
twist desired.

It will be seen that with either of these processes the fiber of the
shell and the spiral ribs lie parallel to each other and are most
perfectly formed to resist the shock of impact, the reaction of which
will be along the line coincident with the resultant of the angular or
rotative and the trajectoral velocities, which line will lie parallel
with the spiral ribs, the pitch of such fiber and r