EXPERIMENTS WITH DOUBLE-BARRELED GUNS AND RIFLES.
The series of experiments we are about to describe has recently been made by Mr. Horatio Phillips, a practical gun maker of London. The results will no doubt prove of interest to those concerned in the use or manufacture of firearms.
The reason that the two barrels of a shot gun or rifle will, if put together parallel, throw their charges in diverging lines has never yet been satisfactorily accounted for, although many plausible and ingenious theories have been advanced for the purpose. The natural supposition would be that this divergence resulted from the axes of the barrels not being in the same vertical plane as the center line of the stock. That this is not the true explanation of the fact, the following experiment would tend to prove.
EXPERIMENTS WITH DOUBLE-BARRELLED GUNS.
Fig. 1 represents a single barrel fitted with sights and firmly attached to a heavy block of beech. This was placed on an ordinary rifle rest, being fastened thereto by a pin at the corner, A, the block and barrel being free to revolve upon the pin as a center. Several shots were fired both with the pin in position and with it removed, the barrel being carefully pointed at the target each time. No practical difference in the accuracy of fire was discernible under either condition. When the pin was holding the corner of the block, the recoil caused the barrel to move from right to left in a circular path; but when the pin was removed, so that the block was not attached to the rest in any way, the recoil took place in a line with the axis of the bore. It will be observed that the conditions which are present when a double barreled gun is fired in the ordinary way from the shoulder were in some respects much exaggerated in the apparatus, for the pin was a distance of 3 in. laterally from the axis of the barrel, whereas the center of resistance of the stock of a gun against the shoulder would ordinarily be about one-sixth of this distance from the axis of the barrel. This experiment would apparently tend to prove that the recoil does not appreciably affect the path of the projectile, as it would seem that the latter must clear the muzzle before any considerable movement of the barrel takes place.
With a view to obtain a further confirmation of the result of this experiment, it was repeated in a different form by a number of shots being fired from a "cross-eyed" rifle,[1] in which the sights were fixed in the center of the rib. Very accurate shooting was obtained with this arm.
A second theory, often broached, in order to account for the divergence of the charge, is that the barrel which is not being fired, by its vis inertia in some way causes the shot to diverge. In order to test this, Mr. Phillips took a single rifle and secured it near the muzzle to a heavy block of metal, when the accuracy of the shooting was in no way impaired.
So far the experiments were of a negative character, and the next step was made with a view to discover the actual cause of the divergence referred to. A single barrel was now taken, to which a template was fitted, in order to record its exact length. The barrel was then subjected to a heavy internal hydrostatic pressure. Under this treatment it expanded circumferentially and at the same time was reduced in length. This, it was considered, gave a clew to the solution of the problem. A pair of barrels was now taken and a template fitted accurately to the side of the right-hand one. As the template fitted the barrel when the latter was not subject to internal pressure, upon such pressure being applied any alterations that might ensue in the length or contour of the barrel could be duly noted. The right-hand barrel was then subjected to internal hydrostatic pressure. The result is shown in an exaggerated form in Fig. 2. It will be seen that both barrels are bent into an arched form. This would be caused by the barrel under pressure becoming extended circumferentially, and thereby reduced in length, because the metal that is required to supply the increased circumference is taken to some extent from the length, although the substance of metal in the walls of the barrel by its expansion contributes also to the increased diameter. A simple illustration of this effect is supplied by subjecting an India-rubber tube to internal pressure. Supposing the material to be sufficiently elastic and the pressure strong enough, the tube would ultimately assume a spherical form. It is a well known fact that heavy barrels with light charges give less divergence than light barrels with heavy charges.
After the above experiments it was hoped that, if a pair of barrels were put together parallel and soldered only for a space of 3 in. at the breech end, and were then coupled by two encircling rings joined together as in Fig. 4, the left-hand ring only being soldered to the barrel, very accurate shooting would be obtained. For, it was argued, that by these means the barrel under fire would be able to contract without affecting or being affected by the other barrel; that on the right-hand, it will be seen by the illustration, was the one to slide in its ring.