Field artillery now began to appear in the form which it was to retain with but a few changes, until the era of the modern field carriage. The cradle disappeared, muzzle-loading guns cast with trunnions taking its place, and a stepped wedge resting on the trail superseded the pin and arc. With the exception of the gun, most parts of these carriages were of wood and were to remain so until 1870, when metal carriages came into general use. Muzzle loading guns had supplanted breech-loaders because of the poor obturation and the many accidents resulting from use of the latter type. Although numerous experiments were made, breech-loading guns did not come into vogue again until 1850, when the experiments of Major Cavalli (1845), the Walnendorff gun (1846) and the Armstrong gun (1854), produced satisfactory types. Up to 1860 practically all guns were smooth bore. Even during the Civil War the smooth bore was generally used, although the rifled gun began to make an appearance and was used in small numbers by both sides at the battle of Gettysburg. Some breech loaders began to appear at the same time. Improvement in the ballistic properties of the gun necessitated a corresponding improvement in the sighting facilities. In 1880 rifled breech loading and built-up steel cannon came into general use. Rifled guns shoot accurately and as a result, improved methods in direct laying were devised. The period between from 1880 to the present, has brought about changes in gun construction which, possibly, have been equaled in importance to artillery only by the present change which is taking place in the means of artillery transportation and self-propelling mounts. In this period in rapid succession came the modern breechblock and with it the rapid firing gun. This brought about the change to the present system of breaking the force of recoil of the gun and restoring it to its firing position without disturbing the position of the carriage. This added to the possibilities of rapid and more accurate fire. Then came the invention and use in the field artillery of smokeless powder. Previous to this time the great amount of smoke produced by the black powder when the piece was fired retarded the rapidity of fire because it enveloped the materiel in a thick cloud of smoke which obscured the target and made it impossible to fire again until the smoke had blown away. It made concealed positions for the artillery almost impossible. The advent of smokeless powder made firing more rapid and made possible the selection of concealed positions. This in turn made indirect fire feasible and necessitated the development of better sights. Indirect fire increased the rapidity of fire and gave to the commanders of firing units a greater control over their fire. With the use of recoil mechanisms and shields for the guns, the cannoneers were permitted to serve the piece continuously—a condition which was impossible with the recoiling carriage.