Modern Use of Black Powder
Aside from gradual improvement in the formula, no
great change in powder making came until 1860, when Gen. Thomas J.
Rodman of the U. S. Ordnance Department began to tailor the powder to
the caliber of the gun. The action of ordinary cannon powder was too
sudden. The whole charge was consumed before the projectile had fairly
started on its way, and the strain on the gun was terrific. Rodman
compressed powder into disks that fitted the bore of the gun. The disks
were an inch or two thick, and pierced with holes. With this
arrangement, a minimum of powder surface was exposed at the beginning of
combustion, but as the fire ate the holes larger (compare fig. 20f), the
burning area actually increased, producing a greater volume of gas as
the projectile moved forward. Rodman thus laid the foundation for the
"progressive burning" pellets of modern powders (fig. 20).
FIGURE 20—MODERN CANNON POWDER. A powder grain has the characteristics
of an explosive only when it is confined. Modern propellants are
low explosives (that is, relatively slow burning), but projectiles
may be loaded with high explosive, a—Flake. b—Strip, c—Pellet. d—Single
perforation, c—Standard 7-perforation, f—Burning grain of 7-perforation
type. Ideally, the powder grain should burn progressively, with
continuously increasing surface, the grain being completely consumed by
the time the projectile leaves the bore. g—Walsh grain.
For a number of reasons General Rodman did not take
his "perforated cake cartridge" beyond the experimental stage, and his
"Mammoth" powder, such a familiar item in the powder magazines of the
latter 1800's, was a compromise. As a block of wood burns steadier and
longer than a quick-blazing pile of twigs, so the 3/4-inch grains of
mammoth powder gave a "softer" explosion, but one with more "push" and
more uniform pressure along the bore of the gun.
It was in the second year of the Civil War that
Alfred Nobel started the manufacture of nitroglycerin explosives in
Europe. Smokeless powders came into use, the explosive properties of
picric acid were discovered, and melanite, ballistite, and cordite
appeared in the last quarter of the century, so that by 1890
nitrocellulose and nitroglycerin-base powders had generally replaced
black powder as a propellant.
FIGURE 21—MODERN POWDER TRAIN FUZE.
Still, black powder had many important uses. Its
sensitivity to flame, high rate of combustion, and high temperature of
explosion made it a very suitable igniter or "booster," to insure the
complete ignition of the propellant. Further, it was the main element in
such modern projectile fuzes as the ring fuze of the U. S. Field
Artillery, which was long standard for bursts shorter than 25 seconds.
This fuze was in the nose of the shell and consisted essentially of a
plunger, primer, and rings grooved to hold a 9-inch train of compressed
black powder. To set the fuze, the fuze man merely turned a movable ring
to the proper time mark. Turning the zero mark toward the channel
leading to the shell's bursting charge shortened the burning distance of
the train, while turning zero away from the channel, of course, did the
opposite. When the projectile left the gun, the shock made the plunger
ignite the primer (compare fig. 42e) and fire the powder train, which
then burned for the set time before reaching the shell charge. It was a
technical improvement over the tubular sheet-iron fuze of the Venetians,
but the principle was about the same.
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