409. Ranges and Time of Flight.—So far as ascertained, are contained in Table VII., Appendix B.
410. Precautions to be Observed.—In the use of these rifled cannon, it is of the utmost importance that all the directions relative to the lubrication of the shell, its being close home, charge and kind of powder used, and lining of the shells, shall be carefully observed.
Many premature explosions of shells having taken place in these guns, which are attributed to various causes, such as,—defects of metal, porosity, faulty fuzes, concussion and friction of the powder within the shell,—it is ordered that, on the occurrence of a premature explosion or rupture of a shell within the gun, it shall be immediately washed out and a careful examination made of the interior of the bore, by the mirror and by taking impressions in wax (see [Mode of Taking Impressions, p. 16, Part III.]), and all the circumstances of the case reported to the Bureau, specifying the kind and calibre of the shells, kind of fuzes, the charge and kind of powder, with its manufacturer's name: and,
Were the shells filled completely, and with what kind of powder?
Were the shells coated inside with any kind of composition?
Are any cracks or marks of scoring visible in the bores?
In rifled cannon, cracks or injuries produced by firing, or the rupture of shells, are to be sought for—thus,
1. Around and in rear of the vent-bouching.
2. On the top of the bore, between the trunnions and reinforce-band.
3. On the lower side of the bore, near the seat of the shot, at the junction of the lands and grooves.
4. Near the inside of the muzzle, caused by explosion of shells.
Although shells have been frequently ruptured in the guns without leaving any visible traces of injury, yet they may be developed after a certain number of rounds. Thus, in proving a gun at West Point, a shell exploded in the gun at the second fire: on examination, no traces of injury could be perceived; but, on a re-examination of the gun after the tenth fire, a fine transverse crack was discovered in the rear of the vent, extending two-thirds round the bore. It is therefore important that frequent examinations shall be made, even if no apparent injuries exist, as it is the opinion of the inventor of the guns that the principal, if not the only cause of failure of these guns in service, is due to the rupture of shells within the bore.
Experiments have been made, and are still in progress, which appear to show that these premature explosions may be to a great extent obviated, if not altogether prevented, by lining or coating the rough surface of the interior of the shell with a smooth and elastic coating.
All rifle-shells, except those for howitzers, before being issued for service, shall therefore be lined or coated on the interior with a mixture composed of—
16 ounces of soap—common yellow, not salt-water soap.
7 ounces of tallow.
7 ounces of rosin.