From the theory we have just given a detail of, it appears that the superior range of long barrels was founded intirely upon the opinion, that the powder fires gradually all the time it is passing through the barrel. The conclusion necessarily drawn from this, was, that the larger the charge, the longer time it was in kindling; and hence, that for any assigned charge, the barrel must be of a proportional length, so that the powder may be completely inflamed just as the ball or shot are about to quit the muzzle: The converse of this proposition was, that in every piece there is a certain charge which will be all fired just at the parting of the ball or shot from the mouth of the piece, and that any addition of powder will not take fire, but will only serve, by its weight, to diminish the action of the rest, and consequently, to retard the velocity of the shot or ball,
If this matter be considered with mathematical rigour, it must certainly be allowed, that, as the fire is not at once applied to every particle of the powder, the whole of the charge cannot be inflamed at the same instant; but it is equally certain, that the progress of the inflammation is so rapid, that the powder is completely kindled before the ball or shot arrives at the mouth of the shortest barrel ever made use of.
To determine this, a number of experiments were made by a committee of the Royal Society, so long ago as the year 1743 and by these it was shewn, that when a barrel was shortened so much that the ball placed before the powder was upon a level with the muzzle, the unfired powder, collected from the discharge, by means of a cloth spread before the piece, weighed but one twelfth of the charge. This was analysed, and found to contain less saltpetre than an equal portion of the same powder did. Hence, and from the extreme minuteness of the particles collected, there was reason to believe, that the grains to which they belonged were less susceptible of inflammation than the rest, owing, perhaps, to some inequality in their mixture: what served in a great measure to prove this, was, that when the charge, and consequently the heat generated during the explosion, was increased, the quantity of unfired powder collected was proportionally smaller. And we may therefore safely conclude, that the powder is completely inflamed before the ball or shot arrives at the mouth of the shortest barrel ever employed.