 The nature of the projectiles also changed during the ironclad period . Initially , the best armor @-@ piercing projectile was a solid cast @-@ iron shot . Later , shot of chilled iron , a harder iron alloy , gave better armor @-@ piercing qualities . Eventually the armor @-@ piercing shell was developed . 
 The nature of the projectiles also changed during the ironclad period . Initially , the best armor @-@ piercing projectile was a solid cast @-@ iron shot . Later , shot of chilled iron , a harder iron alloy , gave better armor @-@ piercing qualities . Eventually the armor @-@ piercing shell was developed . 
The nature of the projectiles also changed during da ironclad period . Initially , tdabest armor @-@ piercing projectile was a solid cast @-@ iron shot . Later , shot of chilled iron , a harder iron alloy , gave betta armor @-@ piercing qualities . Eventually thdarmor @-@ piercing shell was developed .