Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/295

Rh SPORTING GUNS.] The sizes of barrels are designated according to the weight of the solid spherical lead ball which will just fit them, and hence their diameters vary inversely as the cube roots of their numbers. In the case of No 12 bore, the ball fitting it weighs 12 to the pound, and measures 729 in. in diameter. Ounce bullets (No. 16) fit a bore of 662 in. in diameter. Barrels were formerly bored cylindrically, but the experi ments of gunmakers led them to suppose that better shoot ing could be obtained by boring to shapes departing in various ways from the simple cylinder. The first modi fication introduced consisted in enlarging the breech end slightly for about 10 inches ; subsequently the last few inches at the muzzle were enlarged also, so that the barrel really consisted of two frusta of cones, having the smaller ends together, the position of the narrowest part, like many other matters, was dependent on the fancy of the gunmaker. Of late an attempt has been made to reduce the interior form of the barrel to something like a system, and several kinds of &quot; choke &quot; boring have been introduced. The object to be attained with a shot-gun is to so arrange the charge that the pellets shall be uniformly and thickly distributed round the mean trajectory, and shall occupy a small space longitudinally. In fig. 6 a side view of the charge as it passes through the air is given, ab being the mean trajectory. Exact experiments to determine the proportions of the cloud of shot fired from different guns do not exist, but, judging from observation, they will usually not depart greatly from those of the figure. In fig. 7 is seen the ap- ^ ,- pearance of the target, .. - after being struck by the charge. The test of. &quot;, excellence is regularity of pattern, combined f &quot; with penetration; that &quot; &amp;gt; is, a circle of 30 inches. diameter should be so pitted by the shot at 40 yards range that gaps of the size of a small bird should no- where exist, while the individual pellets should retain force enough to penetrate a certain number of sheets of brown paper. As the shot pass along a barrel driven violently forward by the powder gas, it is probable that the edges of the charge are retarded by friction against the sides of the bore, so that the centre portion extricates itself rather sooner than the edges, and travels with a slightly higher velocity. Supposing the charge to retain an average velocity, on reaching the object fired at, of 300 feet per second, and the leading pellets to have gained 10 feet on the hindmost ones, so that the charge is distributed over a length of 10 feet, a period of time of - 3 th of a second will elapse between the blows of the first and last pellet. If the object be stationary, this interval will be almost imperceptible, and the pattern made on the target by the impact of the shot will exhibit no trace of it. But if the object be a bird flying across at the rate of 60 Fi 281 feet per second (about 40 miles an hour), it will traverse a space of 2 feet in the interval, and so will not receive the CARTRIDGE 12 BORE 13 BORE CHAMBER 2 8. FIG. 8. Plain choke. 1 12 BORE 13 BORE II BOREJ , i 13 BORI FIG. 9. Double choke. 1* 12 BORE 2 BORE 13s BORE 28.0 i FIG. 10. Greener s clioVe. charge at all in the manner shown on the target. Figs. 8, 9, 10 show some of the choke bores fancied by different makers. 1 The manufacture of sporting rifles does not greatly differ Sport from that of shot-guns. Greater strength and weight of rifles. barrel are necessary to resist the pressure of the charge, withstand the wedging action of the bullet, and deaden the recoil. The breech-closing action also demands greater strength, but the general arrangements are not different in principle. Rifles for sporting purposes differ from military pieces in being double-barrelled, and in requiring accuracy and penetration at short ranges, instead of a flat trajectory at very considerable distances. Hence they generally re semble the shot-guns in their action, and fire more powder in proportion to the weight of the bullet than military rifles. In fig. 11 the treble grip snap action is shown as specially devised for rifles firing heavy charges. In addition to the holding power thus provided, a piece is sometimes made to FIG. 11. Treble grip snap action. extend from the rib between the barrels, terminating in a projection which catches in a recess in the top of the false 1 No accurate or crucial experiments have as yet been carried out to determine the true action of these forms, but the editor of The Field is now preparing instruments and endeavouring to approach the sub ject in a scientific manner. The general principles, as far as they can be gathered at present, are, that enlarging or relieving the barrel slightly reduces the friction and allows the shot to acquire greater velocity, while choking the barrel at the muzzle has the effect of directing the outer pellets inwards, and so concentrating the charge.. XL 36