, 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,
exceeding by 1,200 pounds the provisional limit of pressure.
At the fifth round the breech block opened with some difficulty, and
an examination showed that the resistance resulted from the diametral
enlargement of the rear plate.
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