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, 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. Directions have been given to correct this defect. The star gauge records show that no material change took place in the diameter of the chamber or the bore. From 30 inches to 54 inches (measured from base of the breech), there was a diminution in diameter of from 0.001 in. to 0.002 in.; in rear of 30 inches there was no change. No enlargement in the shot chamber exceeded 0.001 in. From the bottom of the bore (the beginning of the rifling) to the muzzle the average enlargements were as follows: in. to 6 in., 0.005 in.; 7 in. to 14 in., 0.003 in.; 15 in. to 29 in., 0.002 in.; 30 in. to muzzle, 0.002 to 0.001 in.
After the third round the joint between the D. and D. rings opened slightly on the top, and measured after the 13th round showed that the opening was about 0.004 in. wide. It cannot at present be stated whether or not this opening increased during firing, but the defect has been noted and will be carefully observed. Enough cocoa powder remains to allow a comparison to be made with such brown prismatic powder as may be adopted finally. No firing has been done as yet to test the best position for the bands, but it will take place as soon as enough of some standard powder is obtained to fire ten consecutive rounds.—Army and Navy Journal.
COMBUSTION, FIRE-BOXES, AND STEAM BOILERS.[1]
By JOHN A. COLEMAN.
Mr. Chairman and gentlemen: I was rash enough some time ago to promise to prepare a paper for this occasion, the fulfillment of which prior engagements have absolutely prevented.