Artillerists seek to effect great range by doubling the weight of the gun, and projectile monsters meet us at all points, to become in every case “monster failures.”
I fear that the most important points have been entirely lost sight of. Instead of ascertaining whether we have suited the projectile power to the 8-inch or 56-pounder, so as to get work from it which is now done by the 10-inch, we have, in our anxiety to get range, looked only to the form or material of the gun; vital principles being totally excluded. The construction of the gun being perfect, the question is, can the expellant force be brought to an equal state of perfection?
In order to obtain the best results from a gun, the gun itself must be perfect in construction, and the expellant force must be brought to bear in the best possible manner upon the projectile; and this is to be done by attending to the granulation of the powder, which must be suited to the length of the gun, to its bore, and to the weight of the projectile.
Common-sense, engineering skill, will demonstrate, that according to the weight of matter to be projected must be the nature of the expellant; accumulative—until it has overcome the inertia of that matter, accelerative—until it has communicated to it the highest state of velocity its power is capable of effecting. If, on the other hand, it is inferior to this, science has not extracted from it the full horse-power it contains; and we are uselessly expending force and destroying our engines by undue pressure being exerted on one part, and inferior pressure on another; whilst by a proper distribution of that force, durability of the cannon is insured, and from twenty-five to thirty per cent. more work may be obtained from an equal quantity of powder, provided its granulation be judiciously selected according to the area of the gun.
There is abundant proof that on this engineering question we have hitherto worked by the “rule of thumb;” prejudice having been a stumbling-block, which nothing but stern necessity will remove. The authorities have but just discovered this, although their attention was directed to it several years ago. In the year 1852, I produced before the Small Arms Committee, at Enfield, a portion of gunpowder suited to the expansive rifle; it was tried to a limited extent, and dismissed with the remark, “We don’t think there is much in it.” Experience, however, has demonstrated the truth of my observations, for, in all extreme range shooting with the expansive or “Greenerian”-principled rifles, not only is considerably greater accuracy obtained with it, but an increase of range equivalent to fifteen or twenty per cent.
Another advantage of using gunpowder of a suitable granulation is the absence of sharp recoil; and thus greater accuracy of range is obtained—accuracy of range and steadiness of weapon being inseparable.
Large-grain gunpowder is not only a more effectual expellant than the fine grain, but is much more safe to use, for by using it the risk of bursting the barrel is much lessened; as a very simple illustration will show. If we estimate the force generated by the usual charge of 21⁄2 drachms (I confine the question to the 14-bore gun, for uniformity) to be 5,000 lbs., whether the powder be fine or coarse grain, it follows that the fine powder, igniting so rapidly, will exert all its force on the breech end of the gun; whereas the coarse powder, igniting less rapidly, distributes this force over the whole length of the barrel: hence the greater risk of a gun bursting with fine powder than with coarse. If we suppose the fine powder to be entirely ignited when it reaches half way up the barrel, then the force of 5,000 lbs. is exerted on the lower half of the barrel; but if the coarser grain is not entirely ignited until it reaches the muzzle, then the force of 5,000 lbs. will be distributed over the whole length of the gun.
But this is not all. The fine powder, igniting almost instantaneously, exerts its force in all directions at once, and the barrel may burst at the side before the charge has time to move; whereas the coarse powder, igniting as it does more slowly, first lifts the charge, and then the volume of gas behind it increasing as the powder becomes more thoroughly ignited, sweeps the charge out of the barrel with a velocity increasing towards the muzzle.
If time is not given for the charge to receive the full advantage of the expansive force of the generated air, the force is exerted, not upon the charge, but upon the barrel of the gun itself; and that time is necessary for the full development of this force, is proved by the fact that miners mix their gunpowder with sawdust, in order to diminish the rapidity of its explosion and thus get the advantage of its force in the distance: from the miners, then, let us learn how to obtain the greatest benefit from this force, and waste it not.
There can be no doubt of the importance of this principle; little progress has, however, been effected from want of scientific illustration; let it be defined like that of steam power, and its adoption will follow as a natural consequence.