[Doc Hoy]

A lead ball would be about half again as heavy as an iron ball. This would mean heavier guns to withstand the additional stress. There are already plenty of accounts of the gun explosions meaning that the science of artillery design and material knowledge had advanced only far enough to result in relatively few options to deal with the higher breach pressures of heavier projectiles. With only limited ability to consistently predict breach pressure and the ability of the gun to handle it, the single defence against accidents was a large safety margin. Hence a heavier gun for a heavier projectile and powder charge.

Heavier guns are:

1. more expensive to make. (Iron was scarse)
2. harder to wrestle around on the battlefield. (Note that the heavier guns used at sea...24 and 32 pounders, which also employed iron shot almost exclusively, were much more massive than those used in the field.)