The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 5: Forts and Artillery.
Francis Trevelyan Miller, Ed.

[138] with their introduction into the foreign services. Prior to that time, artillerists and inventors had directed their attention to the production of a projectile on the expanding system. This method of making the projectile take the rifling had been more or less successful with the bullet, and it was hoped that a device could be invented which would permit the use of the same principle with larger projectiles. The board of rifled Ordnance, in 1859, expressed an opinion that such would be the case, with the exception of one member, who recommended the continuation of experiments with flanged projectiles and similar types. However, the Charrin projectile, an expanding type, was adopted at first, but proved to be unsatisfactory and was withdrawn. The introduction of rifled cannon did not simplify the question of calibers.

up to the summer of 1862, there were made, in the arsenals of the Government and in certain private establishments, bronze rifled guns of 3.67 and 3.8 inches, and large numbers of iron rifled cannon of 2.9 and 3.0 inches. There had been already both smooth-bore and rifled guns of 4.62 inches, and guns of 4.5 inches were also made. The great objection to the smaller calibers was that the range was needlessly great, and the shell too small to be of practical value. With the system of expanding projectiles at first adopted, the question of exact calibers was not of such great importance, for by the method used for accommodating the projectile to the rifling, the same shot could be used for both the 3.67-inch and the 3.8-inch gun.

bronze had been adopted as a standard metal for fieldguns in 1841, and served the purpose excellently until the introduction of rifled cannon, when the increased strain due to the imparting of the rotary motion to the projectile proved too great, and the metal was too soft to stand the wear on the rifling. It was then found that wrought iron served the purpose best, and of this material 3-inch muzzle-loading guns were made. On the introduction of breech-loaders, forged steel proved to be more satisfactory. However, many Parrott rifled