In England a safer method of conversion was followed. Guns were bored out, on a scheme proposed in ’63 by Major Palliser, and accurately turned tubes of coiled wrought iron were fitted in them, which were afterwards rifled. The resulting pieces consisted, then, of a wrought-iron inner tube, supported by a surrounding cast-iron jacket against which, on firing, the inner tube expanded. Thus converted, the old smooth-bores were enabled to develop an energy far in excess of their original limit, and so to prolong for some years their period of usefulness. The conversion of the cast-iron guns was seen to be only a temporary expedient. Just as the smooth-bore cannon, after a last effort to overcome iron plates with spherical solid shot of the largest calibre, withdrew from the competition; so, as the thickness of armour increased, the converted cast-iron cannon, with its special armour-piercing shot of chilled iron, soon reached the limit of its power and gave place to the rifled artillery of wrought iron or steel. And now, rifled ordnance having definitely supplanted the smooth-bore, a new struggle arose between the various systems of gunmaking, and more especially between the two rival methods of loading: by the breech and by the muzzle. The prognostications of those who had doubted whether the latter method was suitable for large ordnance were seen to be partially justified. Other nations had already relapsed into muzzle-loading, impressed by the complexity and weakness of the breech-loading systems of Cavalli, Wahrendorf and other inventors. Besides ourselves only the Prussians, the originators of the breech-loading rifled musket in its modern form, continued to trust in breech-loading ordnance. The Italians, following the example of the French and Americans, abandoned the system. “Thus,” said an English authority in ’62, “while, after more than four centuries of trial, other nations were giving up the moveable breech, ... we are still going from plan to plan in the hope of effecting what will, even if successful in closing the breech, be scarcely safe with the heavy charges necessary for smashing armour plates.”[129]