No satisfactory results either with rifling or with the hexagonal bore could be obtained, and as guns became more powerful it was found that the only way of utilising them with the best results was by loading them at the breech instead of at the muzzle. Obviously, a heavy explosive shell could not be rammed down a big muzzle-loader. The old 32-pounder had a muzzle velocity of 1,600 feet per second, and the 40-pounder rifled breech-loader which took its place was of only 1,200 foot seconds, and the muzzle energy was 570 and 400 foot tons respectively. Various methods were employed and were not by any means satisfactory, but when slower burning powders were introduced, the strain upon the gun was less sudden and more cumulative, so that the pressure upon the projectile was exerted to the full as long as it was within the gun and it was then expelled at the muzzle with the greatest force obtainable. A great advance in naval gunnery was made with the appearance of the Armstrong breech-loader. The first breech-loader from this famous firm was a tube gun which was formed to admit of a breech block being dropped in to close the bore and a screw attachment held it fast. From about 1860 the principal guns in use in the Navy of the Armstrong screw type were the 9-pounder weighing 6 cwt., the 12-pounder weighing 8 cwt., the 20-pounder of 16 cwt., the 40-pounder of 35 cwt., and the 7-inch gun, 99½ cwt. The last-named was of 7.2 inches diameter, and fired projectiles weighing 109 lb. All these guns were on the polygroove system. About this time iron or steel gun carriages were introduced for use on shipboard. The Admiralty, for some reason best known to themselves, fancied muzzle-loaders, and obstinately remained faithful to them long after all other naval powers had discarded them as cumbersome and comparatively useless compared with the newer types of breech-loading guns. The newer muzzle-loaders, however, were improvements on the old smooth-bores, and were built on what is known as the Fraser system, and they were far larger than any which had been constructed before. The inner barrels of the Armstrong 12-inch, 9-inch, and 7-inch muzzle-loading guns were of tempered steel, with solid ends; these were strengthened with wrought-iron coils shrunk on; the trunnion ring, breech-piece and cascable, which was screwed into the latter, were solid wrought-iron forgings. The different parts were hooked together with shoulders and corresponding recesses, to prevent their separation. The muzzle-loader of 64 lb. on Fraser’s cheap construction plan consisted simply of a coiled iron tube, having the muzzle part double, but with a triple coil over the breech.