The trunnions, about a caliber in size, were located well forward (3/7 of the gun's length) "to prevent the piece from kicking up behind" when it was fired. Gunners blamed this bucking tendency on the practice of centering the trunnions on the lower line of the bore. "But what will not people do to support an old custom let it be ever so absurd?" asked John Müller, the master gunner of Woolwich. In 1756, Müller raised the trunnions to the center of the bore, an improvement that greatly lessened the strain on the gun carriage.
Figure 26—EIGHTEENTH CENTURY CANNON, a—Spanish bronze 24-pounder of 1746. b—French bronze 24-pounder of the early 1700's. c—English iron 6-pounder of the middle 1700's. The 6-pounder is part of the armament at Castillo de San Marcos.
Figure 27—SPANISH 24-POUNDER CAST-IRON GUN (1693). Note the modern lines of this cannon, with its flat breech and slight muzzle swell.
The caliber of the gun continued to be the yardstick for "fortification" of the bore walls: