The shooting powers of gun barrels are dependent on two circumstances—goodness of metal, and a proper shape of exterior: it cannot be too often repeated, that a gun barrel is a spring, to all intents and purposes; if you add metal, you add stubbornness, and destroy that expansibility, without the existence of which the barrel is, comparatively speaking, useless. Heavy, ponderous barrels do not propel a charge of shot with either that smartness or degree of closeness that a barrel more scientifically constructed does; you have less recoil certainly, but the addition of half an inch of more metal behind the butt of the breech would do this more effectually, and save you carrying an additional weight. The gradual ignition of powder obviates the necessity of a great thickness of metal in the sides of the barrels; but if it is determined to persevere in the use of peculiarly fine grained powder, you would certainly be justified, nay, required, to have more and better metal than at present, for the electrical nature of the explosion will throw upon the tube that force which would be more judiciously employed in giving impetus to the charge of projectiles.
I have found that expansion will increase the shooting powers of a barrel; but then it must not be the expansion of an unelastic piece of metal, but of metal whose elasticity rebounds with a force equal to that with which it expands; for whatever else you may obtain by creating friction, by boring the breech end of the barrel wider you obtain a greater expansion, as it no doubt has that tendency. We find it an invariable fact, that when barrels are very heavy, compared with their size of bore (if a cylinder), they shoot weak. Also, when barrels are made of irons of different temperatures, where one is placed to prevent the expansion or springing nature of the other, they are never found to shoot well. As a proof of this fact, let any one take the best barrel he ever shot with, and encase it with lead very tight; fire it at a dozen sheets of paper, and see if the effect be equal to what it was when the barrel was unencumbered. On the contrary, it will be found to have shot very weak, though close. Let him then examine the lead; and, if any moderate substance, he will find that the explosion has enlarged it considerably. This experiment I have tried repeatedly, and can vouch for its truth.
The proof of barrels is another fact corroborating the truth of our assertion. What else can occasion the bulging, but the expansion? Where the barrels are possessed of soft and hard portions (which is the result of different tempers of different metals), one expands further than the other, and then, of course, the soft part receives no assistance from the hard, and it does not return to its original state.
Put on a barrel, from the breech end to the muzzle, a number of rings of lead; be sure you have them tight, and not further apart than three or four inches; fire that barrel with a usual charge, and if it be a correct taper for shooting, it will have expanded the whole of the rings an equal distance.
From the observations already made, the reader will perceive that the shooting of all barrels depends on a certain degree of friction. The degree of friction necessary, varies according to the nature and substance of the metal. Those metals that require least shoot best. The object of the friction is to create a greater force, by detaining the charge longer in the barrel. If, then, there should not be an extra quantity of powder to consume, the friction would be a decided evil.
This may be understood by rifle practice, in which we find that a short barrel of eighteen inches, with a certain charge, will throw a ball as straight, and quite as strong, or stronger, than a barrel of three feet, loaded with a similar charge. I account for this fact thus: the barrel of eighteen inches will burn all the powder put into it; the long one can do no more. As soon as the ball has left the short barrel, it meets with no impediment but the air. By the time the ball in the longer one has travelled eighteen inches the powder is all consumed; the volume of air in the remaining eighteen inches acts as a destroyer of the force given to it, and it naturally drops its ball short of the other. Increase the charge of powder to as much as the long one can burn, and then it will throw its shot to nearly twice the distance of the other.
An addition of powder beyond the quantity the barrel can consume is disadvantageous; the reverse will be found equally so. Thus it is with fowling-pieces. The quantity of powder that a gun would burn in the shape of a cylinder, would be too little, when, by altering that shape, you increase the friction. The quantity must, therefore, be increased, or this friction will diminish the force of the shot. It is on this that the mistaken supposition is founded, that short barrels will shoot as far as long ones. It is true that with a small charge, or very fine powder, the short barrel will kill at the distance of thirty yards, as well as the long one; but put in the long one as much powder as it can consume, then try the two at twice the distance, and you will find out the mistake under which you have been labouring.
It is on the nature of the metal that the goodness of the shooting principally depends. That barrel which is possessed of the greatest degree of elasticity and tenacity, will throw its shot strongest and closest with the least artificial friction. It is on the knowledge of the qualities and temperatures of the various irons, and on practice in the art of shooting, that a man’s ability in making guns shoot with precision must rest. All plans are merely methods by which an unscientific maker has most frequently succeeded. It would be no difficult task to produce a hundred barrels which will shoot nearly alike; yet every barrel shall be different in its bore.