inch.

[Illustration: THE ARMY 8 INCH STEEL GUN WITH CARRIAGE.]

The breech mechanism is modeled after the De Bange system. The block
has three smooth and three threaded sectors, and is locked in place by
one-sixth of a turn of a block, and secured by the eccentric end of a
heavy lever, which revolves into a cut made in the rear breech of the
gun. The gas check consists of a pad made of two steel plates or cups,
between which is a pad of asbestos and mutton suet formed under heavy
pressure. The rifling consists of narrow grooves and bands, 45 of
each. The depth of the groove is six one-hundredths of an inch.

Although the gun is designed for a charge of 100 pounds, it is
believed that it can be increased to 105 pounds without giving
dangerous pressure, and the intention is to increase the charge to
that amount when the new powder is received from Du Pont.

The following is a very full synopsis of the official report of the
preliminary firings--13 rounds--with this gun:

The first seven rounds were fired with German cocoa powder, which was
received from Watervliet Arsenal. There were two kinds of cartridges,
one kind weighing 85 pounds, and having 30 grains in each layer, the
other weighing 100 lb., and having 27 grains in each layer. In two of
the first seven rounds the weight of the charge was 65 pounds, the
projectiles weighing 182 and 286 pounds; in the next two rounds
charges of 85 pounds were fired, the projectiles, as before, weighing
182 and 286 pounds, while in the last three of the rounds fired with
cocoa powder the charge was 100 lb., while the weight of the
projectile was 182, 235, and 286 pounds. At the seventh round was
fired the normal charge, 100 lb. of powder and a projectile weighing
286 pounds, for which the gun was designed. The mean pressure for this
round, determined by two crusher gauges, was 32,800 pounds, and the
velocity at 150 feet was 1,787 feet.

Two kinds of Du Pont's brown prismatic powder, marked P.A. and P.I.,
were then fired. With the normal charge of P.A. powder (round 12 of
the record), the mean pressure was 35,450 pounds, the velocity at 150
feet was 1,812 feet. For P.I. powder (round 13 of the record), the
pressure was 26,925 pounds, the velocity was 1,702 feet, and a
considerable amount of unconsumed powder was ejected, showing that the
P.I. powder is not a suitable one for this piece. The highest pressure
indicated with the normal charge of P.A. powder was 36,200 pounds,
ex