AIR-Gun, a pneumatic machine for exploding bullets, &c. with great violence.
The common air-gun is made of brass, and has two barrels; the inside barrel A, fig. 1. which is of a small bore, from whence the bullets are exploded; and a large
barrel ECDR on the outside of it. There is a syringe SMNP fixed in the stock of the gun, by which the air is injected into the cavity between the two barrels through the valve EP. The ball K is put down into its place in the small barrel, with the rammer, as in any other gun. At SL is another valve, which, being opened by the trigger O, permits the air to come behind the bullet, so as to drive it out with great force. If this valve be opened and shut suddenly, one charge of condensed air may be sufficient for several discharges of bullets; but if the whole air be discharged on one single bullet, it will drive it out with a great force. This discharge is effected by means of a lock, fig. 2. placed here as usual in other guns; for the trigger being pulled, the cock will go down and drive the lever O, fig. 1. which will open the valve, and let in the air upon the bullet K.
The Magazine Air-gun was invented by that ingenious artist L. Colbe. By this contrivance ten bullets are so lodged in a cavity, near the place of discharge, that they may be drawn into the shooting-barrel, and successively discharged so fast as to be nearly of the same use as so many different guns.
Fig. 3. represents the present form of this machine, where part of the stock is cut off, to the end of the injecting syringe. It has its valve opening into the cavity between the barrels, as before. KK is the small shooting-barrel, which receives the bullets from the magazine ED, which is of a serpentine form, and closed at the end D when the bullets are lodged in it. The circular part abc, is the key of a cock, having a cylindric hole through it, ik, which is equal to the bore of the same barrel, and makes a part of it in the present situation. When the lock is taken off, the several parts Q, R, T, W, &c. come into view, by which means the discharge is made by pushing up the pin Pp, which raises and opens a valve V, to let in the air against the bullet I, from the cavity FF; which valve is immediately shut down again by means of a long spring of brass, NN. This valve V being a conical piece of brass, ground very true in the part which receives it, will of itself be sufficient to confine the air.
To make a discharge, you will pull the trigger ZZ, which throws up the feet ya, and disengages it from the notch a, upon which the strong spring WW moves the tumbler T, to which the cock is fixed. This, by its end u, bears down the end v of the tumbling lever R, which, by the other end w, raises at the same time the flat end of the horizontal lever Q; and by this means, of course, the pin Pp, which stands upon it, is pushed up, and thus opens the valve V, and discharges the bullet. This is all evident from a bare view of the figure.
To bring another bullet to succeed that marked I, instantaneously, turn the cylindric cavity of the key of the cock, which before made part of the barrel KK, into the situation ik, so that the part i may be at K; and hold the gun upon your shoulder, with the barrel downwards, and the magazine upwards, by which means that bullet next the cock will fall into it out of the magazine, but go no farther into this cylindric cavity than the two little springs s s, which detain it. The two circles represent the cock-barrel, wherein the key abovementioned turns upon an axis not represented here, but visible in fig. 4. This axis is a square
piece of steel, on which comes the square hole of the hammer H, fig. 5.; by which the cylindric cavity mentioned is opened to the magazine. Then opening the hammer, as in that figure, the bullet is brought into its proper place near the discharge-valve, and the cylindric cavity of the key of the cock again makes part of the inward barrel KK.
It evidently appears how expeditious a method this is of charging and discharging a gun; and were the force of condensed air equal to that of gunpowder, such an air-gun would answer the end of several guns.
In the air-gun, and all other cases where the air is required to be condensed to a very great degree, it will be requisite to have the syringe of a small bore, viz. not exceeding half an inch in diameter; because the pressure against every square inch is about 15 pounds, and therefore against every circular inch about 12 pounds. If therefore the syringe be one inch in diameter, when one atmosphere is injected, there will be a resistance of 12 pounds against the piston; and when 10 are injected, there will be a force of 120 pounds to be overcome; whereas ten atmospheres act against the circular half-inch piston (whose area is only one-fourth part so big) with only a force equal to 30 pounds; or 40 atmospheres may be injected with such a syringe, as well as 10 with the other. In short, the facility of working will be inversely as the squares of the diameter of the syringe.