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kinson's, on the other hand, there is an oval chamber, one end connected with the nipple, and the other being contracted so as to retard the ignition.
Great stress is laid upon the form of the breech by all the advocates of the muzzle-loader; and they assert that if the powder is burnt in a chamber of the same size and form as the barrel itself, with a mere closure at right angles, the effect is greatly deteriorated. I have tried the experiment myself, firing the same barrel with different breeches, but I confess I have not been able to obtain any very reliable conclusions. As far as my experience goes, the barrel is all in all; and so long as the breech is sound, and the ignition perfect, it matters comparatively little what shape the chamber may bear. It is very commonly supposed that the recoil is materially increased when the powder is fired anywhere but at its posterior part; but this is now proved to be a myth, and, according to the experiments made by the Board of Ordnance, the recoil is least when the centre of the charge is tired. The Prussian needle-gun, also, in which the ignition is in front, is remarkable for the absence of recoil ; so that, I think it may fairly be assumed that the point of ignition has no reference to recoil. There is also another point which requires consideration-namely, whether it is desirable to allow of a vent for the explosive gases at the end of the cross-hole? The proposed object is to lessen recoil, and until very recently most of the better classes of guns were made with a vent hole,” lined with platina to prevent corrosion; but the plan is now almost entirely abandoned, being found to be quite inoperative. The grains of the powder enter the fine hole, and fill it up even prior to the first discharge ; but subsequently it is quite closed by the residuum left after the explosion.
In the ordinary percussion gun, which is that now being described, the powder in the chamber is ignited by exploding a cap upon a nipple, whose canal communicates with the cross-hole of the breech, or, in some cases, with the chamber itself. The nipple in either case is of a conical form ex
ternally for about the third of an inch, so as to allow of the copper cap securely clipping it; next to this cone is a shoulder, which is square, or, what is better, a rectangular oblong, so as to admit of the application of a key for its removal. Beyond this, again, it is tapped, and forms a male screw, which is accurately adapted to a female screw cut in the breech. Thus, then, there are two things to be considered in reference to the nipple-1st, its own shape; and 2ndly, the direction in which it is screwed into the breech.
The nipple itself should be of good steel not tempered too highly or it will break. The best kind is bored so as to present two cones, one short and external, and the other longer and internal, the communication between the two being small and lined with platinum to prevent the corrosion, which would otherwise soon fill it up; and then comes the pricker, which removes the rust and enlarges the aperture so much that a great part of the gas escapes through it. Ordinary
nipples present only one cone, the base of which may be external (fig. 26 a), or internal (fig. 266); the former being greatly to be preferred with good caps, as it allows a full volume of flame to be driven down upon the charge. The platinated nipple
is more expensive than the common one, NIPPLES. (FULL SIZE.)
and it is apt to lose the ring of platina, but as long as this adheres it will be serviceable; still for common purposes nothing answers better than the form shown in fig. 26 a.
In adapting the nipple to the breech, a hole is sometimes drilled in a slightly oblique direction down upon the end of the chamber. This was first proposed, I believe, by Mr. Greener, as his “centric" method of firing, but as adapted by him it was found to weaken the handle of the stock too much, and he has abandoned its use in consequence. Another maker (Mr. Horton of Whitehaven, late of Birmingham) has re introduced it as his “eccentric breech," the only difference being that the nipple enters more obliquely and the hammers also fall in a corresponding direction, so that the stock is not weakened to the same extent. But though the latter is improved the breech itself is still weakend at this part, whether
sufficiently so to make it dangerous experience alone can determine. It is certainly an improvement upon Mr. Greener's original plan, and as such is introduced here:
On comparing this with the ordinary breech (fig. 24, p. 234) it will at once be seen that in Horton's plan the nipple is brought nearer to the charge, and may possibly be more liable to be blown out, but with proper care in tapping I have no doubt such an accident would never occur. That the firing is sharper I fully believe from theoretical calculation, but whether in practice the difference would be discovered I do not pretend to say. One advantage is possessed by Horton's breech-viz., that a pin or pricker may be passed straight down into the chamber, and thereby any accumulation may with certainty be disposed of; whereas, in the cross-hole it meets with an angle, and cannot get any further. In the gun-trial of 1858, a gun made on this plan was shot by Mr. Horton and performed well, though from his nervousness the shot from the first barrel almost entirely missed the target.
The lock of the percussion gun is a very simple and efficient piece of mechanisin, having for its object to explode the cap on the nipple by means of a sharp blow, which must be so arranged as to finish with its greatest amount of strengths so as to prevent the hammer from being blown up
PERCUSSION GUN LOCK. (HALF SIZE.) again by the force of the explosion. The following are the parts of which this lock is composed, which are the same in number and principle whether it is what is called a “back actioned" lock or not, beginning with
The lock plate and bridle, which when screwed together, form the skeleton (fig. 29
LOCK PLATE AND BRIDLE. (HALF SIZE.) The cock, or striker (fig. 30 a), which rises and falls outside the plate in unison with the tumbler (6), a piece of iron
MAINSPRING AND SWIVEL.
of a peculiar shape lying be
Fig. 3). tween the plate and the bridle, and acted on through the swivel a (fig. 31, a), by means of the mainspring (fig. 31, b c), which is attached to the plate in its upper
half. It will be seen on examination, that by the pecu- (HALF SIZE.) liar form of the tumbler and swivel, the lever upon which the spring acts is longer when the striker is down on the nipple than at full or half-cock, and thus it exerts its greatest force in that position. In the back of the tumbler (6) are two notches or“ bents," one deeper than the other, which are intended to receive the scear. This and its spring (fig. 32) are both attached to the bridle, lying between it and the plate, and working upon two screws, which pierce them. The scear has a sharp tooth which drops into the notches of the tumbler one after the other, and is kept there by the spring. When the scear is dropped into the half-cock bent, this is so deep that it cannot be depressed out of it by raising the other end by means of the trigger, and consequently the gun cannot be fired in that position. But at full cock the notch is much shallower, and a force usually equal to about 3 or 4lbs. will disengage it when applied to the trigger. The side nail is the screw which attaches the lock to the stock, through the hole drilled in the plate in front of the cock. This lock may therefore be considered as consisting of four important divisions:-(a) the skeleton or plate and bridle; (6) the cock and tumbler; (c) the mainspring and swivel; and (d) the scear and scear spring.
(a.) The shape of the plate has three chief variations-one the fore-actioned bar-plate, being that which is engraved above, and which is now generally used for best guns, the front part being accurately fitted to the barrel. In the old plan there was a thin layer of the stock intervening, which was apt to be splintered; but this is only now used for cheap guns, in which the wood is made to cover bad workmanship. The back-actioned lock, as shown in the Lefaucheaux gun