Projectile Shape

• Smooth-bore cannons can fire sphere-shaped cannonballs.Jupiterimages/Photos.com/Getty Images
  
  A smooth-bore cannon barrel has no rifling -- spiral grooves lining the inside of a gun barrel. The rifling process imparts spin to a projectile, increasing range and accuracy. Projectiles fired from a smooth-bore cannon must have a stable shape, such as the sphere shape of pre-modern cannonballs or the fin shape of mortar rounds.
  
  

Canister Rounds

• Civil War-era smooth-bore cannonJupiterimages/Photos.com/Getty Images
  
  During the American Revolution and Civil War, smooth-bore cannons were highly effective in employing canister rounds, which were thin-skinned metal projectiles full of small, lead bullets. Canister rounds essentially turned cannons into giant shotguns. Smooth-bore cannons were also prevalent on Civil War battlefields because they were less expensive and easier to produce than the more rare rifled cannons.
  
  

Less Gunpowder, Longer Life for Anti-Tank Guns

• Modern smooth-bore anti-tank gunsScott Nelson/Getty Images News/Getty Images
  
  Smooth-bore cannons are still in use in modern weapon systems, particularly as anti-tank guns. Because modern tanks have much thicker armor than their W.W. I and W.W. II counterparts, rifled projectiles must have increased muzzle velocity with a larger charge in order to penetrate the armor. This leads to the use of massive amounts of gunpowder, which ruins the cannon barrel much more quickly than otherwise. Smooth-bore cannons, however, require a much smaller amount of powder to achieve the same velocity, and the barrels are not ruined nearly as quickly. Fins and electronic fire-control systems increase modern smooth-bore accuracy.
  
  

Portability and Simplicity of Mortars

• Modern smooth-bore mortarScott Olson/Getty Images News/Getty Images
  
  Modern mortars are also smooth-bore weapons and function as smaller cannons that a single soldier can carry and set up. They have the advantage of being portable and simple to fire; the soldier needs only to adjust the angle of the mortar tube and drop the projectile down the smooth bore of the barrel. Mortars' basic design hasn't changed since W.W. I, although larger mortars were used as far back as the Civil War. A mortar fires a low-velocity, short-range finned projectile, and they are often used in closeup, small-unit action.
  
  

Large-Area Dispersement for Shotguns

• Modern shotguns have a smooth bore.Jupiterimages/Photos.com/Getty Images
  
  Some modern personal smooth-bore weapons also have advantages over their rifled counterparts. The shotgun is a smooth-bore, hand-held weapon that fires a load of small, individual pellets that disperse over a large area due to the lack of rifling in the gun barrel. The effect is very similar to that of a canister round.