Chapter V: Rifled Cannon

384. The rifled cannon at present in service are--

PARROTT.

-------------------------+-------+--------------------+---------+---------+ DENOMINATION. |WEIGHT.| CHARGE. | WEIGHT | WEIGHT | | | | OF | OF | | | | SHELL. | SHOT. | -------------------------+-------+--------------------+---------+---------+ | lbs. | | | | 6.4-inch, or 100-pounder | 9,700 | 8 lbs. rifle. | 80 lbs. | 70 lbs. | 5.3-inch, or 60-pounder | 5,400 | 6 lbs. rifle. | 50 lbs. | 60 lbs. | 4.2-inch, or 30-pounder | 3,550 | 3-1/4 lbs. cannon. | 29 lbs. | 30 lbs. | 3.67-inch, or 20-pounder | 1,750 | 2 lbs. cannon. | 18 lbs. | 20 lbs. | -------------------------+-------+--------------------+---------+---------+

DAHLGREN.

-------------------------+-------+----------------+---------+----------+ DENOMINATION. |WEIGHT.| CHARGE. | WEIGHT | CHARGE. | | | | OF | | | | | SHELL. | | -------------------------+-------+----------------+---------+----------+ | lbs. | | | | 4-inch, or 20-pounder, | | | | | bronze howitzer | 1,340 | 2 lbs. cannon. | 18 lbs. | 0.86 lb. | 3.4-inch, or 12-pounder, | | | | | bronze howitzer | 880 | 1 lb. cannon. | 11 lbs. | 0.50 lb. | -------------------------+-------+----------------+---------+----------+

385. CHARGES FOR PARROTT'S SHELL.

-----------------+----------+----------+----------+----------+---------+ | 8-INCH. | 100-PDR. | 60-PDR. | 30-PDR. | 20-PDR. | -----------------+----------+----------+----------+----------+---------+ | lbs. oz. | lbs. oz. | lbs. oz. | lbs. oz. | lb. oz. | Long | -- | -- | 3.4 | 1.8 | 1. | Short | -- | 3.11 | 2.2 | -- | -- | -----------------+----------+----------+----------+----------+---------+

386. SHELL AND SHOT GAUGES.

---------------------------+----------+----------+----------+----------+ | 100-PDR. | 60-PDR. | 80-PDR. | 20-PDR. | ---------------------------+----------+----------+----------+----------+ Greatest | 6.36 | 5.27 | 4.17 | 3.64 | True diameter | 6.35 | 5.26 | 4.15 | 3.63 | Least | 6.33 | 5.24 | 4.14 | 3.61 | ---------------------------+----------+----------+----------+----------+

387. In the rifle-guns of Mr. Parrott, provisionally adopted, it is intended to retain the full charge of powder which a smooth-bore gun of the same calibre would have with a round shot. The projectile for the rifled gun is to be usually ten times the weight of this charge.[41]

388. To obtain greater initial velocity, projectiles of less than the full weight have been provided--solid shot of 70 pounds for the 100-pounder, with the front end "chilled." Such projectiles, though not suited for long ranges, will be effective at 1,000 yards or less, and are well calculated to act against oblique surfaces of iron.

389. The powder for the 100-pounder and 60-pounder should be of Rifle (or, as formerly called, No. 7):--for the smaller calibres, 30-pounder and 20-pounder, of Navy cannon powder. The cartridge-bags are the same as those prescribed for similar calibres of smooth-bore guns.

390. The Parrott guns have been arranged for the use of a certain kind of projectile, supplied by the inventor. These have reference not only to the calibre and mode of rifling, but to the design of the gun itself. For these reasons, the inventor objects to the use of any other than his own form of projectile in the guns of his invention. This request has been acceded to in the heavier calibres. The shells of Schenkl and Hotchkiss have also been used, however, in the smaller calibres.

It is not considered expedient to describe these projectiles, and it is therefore directed that the Commander, Executive Officer, and Gunner shall make themselves thoroughly acquainted with their construction, and the percussion and time fuzes issued with them, before sailing. The Ordnance Officer will furnish them with any information on these subjects in his possession.

391. The projectiles consist of shells, shrapnel, and solid shot. All rifled projectiles used in the Navy are of the expanding class; that is, forced into the grooves by the action of the charge of powder, and require no other precautions in loading than common spherical shells.

392. It is, however, essential--

1st. That the base of every rifle-projectile, especially the Parrott, shall be thickly greased before entering it into the gun.[42] For this purpose common pork slush, prepared by several washings in hot fresh water, may be used.

2d. That the bores of all guns shall be frequently washed, the grooves of rifled guns cleaned of all residuum and dirt, and a moist sponge invariably used. After firing, the bore should be oiled with a sponge.

The attention of Commanding Officers is especially called to this requirement; and the Bureau desires that the action of Parrott's and other rifle-projectiles fired under the above conditions, may be carefully observed and reported; for it is believed that nearly all the failures of projectiles in actual service result from the grooves being filled, after a few rounds, with a hardened residuum of powder.

393. It is also necessary that the shell shall be close home on the powder, otherwise the necessary expansion will not take place, and the shell will tumble immediately after leaving the gun, utterly destroying its range and accuracy.

394. In order to be certain that the projectile is properly home, the rammer-handle must be marked to indicate it.

395. It is very important that dirt, sand, or other foreign substances should not be carried into the gun on the sponge or the projectile, or by the wind in batteries on shore.

In using guns on shore, a canvas muzzle-bag, a soft wad, or a light stopper of wood, suggest themselves as means of security during the interval between loading and firing the gun. The cover or stopper might be removed, or left to be blown away at each discharge.

The longer the interval above alluded to, and the higher the elevation at which the gun is kept, the more important and necessary are these precautions.

396. Much care is taken to give the projectiles uniformity of size; and if the powder is of suitable quality, those now supplied will almost invariably take the grooves. Should difficulty in this respect, however, be experienced, it may be remedied by separating the brass ring from the iron at three or four points of the circumference. This should be done with a cold chisel, very slightly, and so as not to interfere with the loading. It is only necessary to sever the contact of the two metals.

397. As the projectile slides in the gun with very little friction, particularly when greased, the gun should therefore be elevated and eased out when firing to leeward, that the shot may not be started from its seat. An experiment to test this, showed that running a 100-pounder out with the force of its crew against the forward hurter, the gun being level, started the shot forward nearly two feet.

Placing a grommet or other wad over elongated projectiles is positively prohibited.

398. The 100-pounder and 60-pounder guns being, respectively, of the calibres of the 32-pounder and 18-pounder spherical shot, and fired with the same charges, these shot may be fired from them with excellent effect, particularly on ricochet. The round shot should be sewed up in canvas or felt, strapped to a sabot, or snaked between two grommet-wads.

399. Both percussion and time fuzes are supplied for these rifle-guns. When the object to be fired at presents a sufficient resistance, such as masses of timber or earth, ships, or solidly-built houses, the percussion-fuzes alone should be used from rifled cannon. They will, however, frequently fail to explode the shell at long ranges, owing to the shell not striking on its apex; or, if fired into loose earth, which checks its momentum too slowly to make the plunger strike with sufficient force.

400. It has been observed that time-fuzes burn with greater rapidity in shell thrown from rifled cannon. Being in front, they are subjected to greater pressure from the air. A similar effect is produced when the fuze is confined under a water-cap, as in the naval time-fuze.

401. The fuze-holes of the heavy shells are cast larger than the diameter of the regular fuze-stocks of the navy, which can, however, be used with the aid of a bouching or an adapting ring, always sent with the shells.

This bouching has heretofore been made of cast zinc. Others with a flange and washer and the thread cut are now supplied, and the use of the old rings is prohibited.

402. If it be desired to explode the shell in front of or in the midst of a body of troops, or after having penetrated some resisting obstacle, the time-fuze should be used. This is the only fuze to be used with shrapnel.

403. The Vent is made in a bouching of pure copper screwed into the gun. In the largest calibres the interior orifice is lined with platinum.

The upper portion of the copper in naval guns is replaced by steel, to obtain a harder surface for receiving the blow of the hammer. The steel is three-fourths (3/4) of an inch thick.

A new vent can be readily put in, after getting out the old one, without injury to the screw-thread. This can be done by boring out the bouching with a drill, which leaves a thin shell containing the thread. Into the hole thus made insert a square mandrel about four inches, driving it lightly; by wrenching it, a portion of the shell of the bouching can be detached and removed by unscrewing. This may be repeated, and the whole of the old copper removed. The screw-thread is then to be cleaned out, and the new vent-plug screwed in.

404. SIGHTS.--These consist of a fixed sight upon the right rimbase, and a brass movable sight placed in a socket which is screwed into the rear of the reinforce at the breech of the gun. The movable sight is furnished with a sliding eye-piece, and is graduated up to 10 deg.. The eye-piece is also capable of lateral adjustment to allow for the drift as far as 10 deg., and for the effect of the wind. It is desirable that the sights should be placed on both sides of the breech; otherwise, in firing from a port at extreme train, there is a considerable loss of lateral aim. Furthermore, with the sight on the right rimbase, it is not convenient for the 2d Captain to attend the screw without interfering with the aim.

405. These guns are all rifled to the right, by which it is understood that the upper surface of the projectile is made to turn from left to right, the observer looking from the breech towards the muzzle of the gun.

406. DRIFT.--This is a deviation caused by the direction of the rifling, is always to the right when uninfluenced by the wind, and is to be allowed for.

407. The drift is in practice confounded with the deviation produced by the direction and force of the wind, which may either annul or increase it, according to whether it blows from right or left across the line of fire. At long range it is also necessary to consider the motion of the vessel across the line of fire. Suppose this to be at the rate of six knots, and the gun is elevated 15 deg., the time of flight would be by the Tables, 18 sec., while the deviation arising from this cause would be upwards of 60 yards. It is therefore of great importance that the Captain of the gun shall be carefully instructed in making this adjustment of the eye-piece.

408. ELEVATING SCREW.--To obtain readily the changes of elevation necessary in the use of rifled cannon, the heavier calibres are made with very small preponderance, and are supplied with an elevating screw which is attached to the carriage at the lower end, while the nut is connected with the cascabel of the gun. Both screw and nut admit of movements by which the screw can take any position required in the various degrees of elevation. The parts should be allowed a certain amount of play; if binding is prevented, it is believed that the evident advantages of the screw may always be obtained.

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.

The tallow should be melted first, then melt and add the rosin, and, lastly, the soap, bringing the mass to a heat that will make it _very_ fluid.

The shells having been first thoroughly cleaned, fill them about one-third full of the composition, roll them slowly so as to spread the mixture over the whole interior surface, and then pour off the residue. This coating should be about five-hundredths (0.05) of an inch in thickness, and is expected, from a series of experiments made for the purpose, to prevent the premature explosion of shells in the bores of rifled guns.

The Bureau further directs that hereafter the charge of the 100-pounder, or 6.4 inch, Parrott rifle, shall be reduced to eight (8) pounds of rifle, or No. 7 powder, and that only the short shell or solid shot, not exceeding eighty (80) pounds weight, and spherical projectiles, prepared as directed in the Circulars of February 24th and July 6th, 1864, be used in this gun.

411. EXTERIOR DIMENSIONS OF BOXES CONTAINING PARROTT'S PROJECTILES.

--------------------------------+---------+---------+--------- | LONG. | WIDE. | HIGH. --------------------------------+---------+---------+--------- | Inches. | Inches. | Inches. 100-pounder, short 1 | 18-3/4 | 8-3/4 | 8-3/4 60-pounder, | | | 30-pounder, containing 10 | 25-1/4 | 11 | 15-3/4 20-pounder, containing 10 | 25-1/4 | 10-1/2 | 13 --------------------------------+---------+---------+---------

412. HOTCHKISS'S PROJECTILE FOR 20-POUNDER AND 12-POUNDER HOWITZER.

--------------------------------+---------+---------+--------- 20-pounder, containing 5 | 24 | 12 | 6-1/2 12-pounder, containing 10 | 20 | 9 | 9 --------------------------------+---------+---------+---------

413. SCHENKL'S PROJECTILE FOR 20-POUNDER AND 12-POUNDER HOWITZER.

--------------------------------+---------+---------+--------- 20-pounder, containing 5 | 24 | 14 | 7 12-pounder, containing 10 | 22-1/4 | 9-1/2 | 11-1/2 --------------------------------+---------+---------+---------

414. J.A.D. PROJECTILE FOR 20-POUNDER AND 12-POUNDER HOWITZER.

--------------------------------+---------+---------+--------- 20-pounder, containing 3 | 15 | 12-1/4 | 7 12-pounder, containing 5 | 19 | 10-1/4 | 6 --------------------------------+---------+---------+---------

FOOTNOTES:

[41] Owing to the recent accidents which have taken place with these guns, the 150-pounder has been withdrawn from service, and the charge of the 100-pounder provisionally reduced to eight (8) lbs. of Rifle powder, and the short shell of eighty (80) lbs. only is to be used.

[42] The Schenkl, Hotchkiss, and some other projectiles, have a small quantity of grease attached.