65. So long as the wear is regular, and the cracks, although numerous, do not exceed .5 of an inch in length, the indications are good. If the cracks are but few or diminish in number, running into each other and extending rapidly, it is a very unfavorable sign. In the rifle cannon (Parrott's) cracks athwart the bore either running into the bouching or in the rear of it are very unfavorable to the gun's endurance.
66. Whenever any premature explosions of shells take place within the gun or near the muzzle, a careful examination of the gun shall be made; and all the circumstances of the case, together with the opinions of the commander and officers in immediate charge as to the cause thereof, reported to the Bureau; taking care to state the kind of shell and species of fuze used; the mode of loading; whether the shell was lined or coated on the interior; kind, charge, and name of maker of the powder which was used in the gun and shell.
There is reason to believe that few failures of the Parrott rifles have occurred where the guns have not been previously, or at the time, injuriously strained by the explosion of shells within the bore.
67. Whenever a gun shall give away under fire, or an accident of any kind happen to one, the Bureau desires to be immediately informed of all the facts in relation thereto.
Particular attention should be paid to the following points:
1. The manner in which the gun was loaded, stating the charge and kind of powder used, and character and weight of projectiles.
2. The condition and appearance of the gun after it gave way, and what effect was produced on the carriage by the explosion.
3. What injuries, if any, occurred to the crew of the gun or vessel.
Sketches of the gun and fragments which remain should also be sent to the Ordnance Yard at Washington for trial of density and tensile strength, accompanied by the written statement in detail of the officers in immediate charge of the gun, and if practicable a photograph should be taken.