A smoothbore is a firearm or artillery barrel that does not contain rifling—the spiral grooves cut into a bore to impart spin to a projectile. By contrast with rifled barrels, smoothbores present an entirely smooth interior surface. Smoothbore designs appear across a wide spectrum of weapons, from handheld shotguns to heavy mortars and some modern tank guns. For background on the contrasting technology, see rifling.

Key characteristics

Smoothbore barrels are defined by the absence of grooves that would otherwise stabilize a projectile by spin. That simple structural difference produces several practical effects that influence performance and use:

  • Simpler manufacturing and cleaning compared with rifled barrels.
  • Greater suitability for firing multiple small projectiles (shot) that spread on departure from the muzzle.
  • Lower inherent accuracy for single, spin-stabilized projectiles unless other stabilization methods (fins, sabots) are used.
  • Compatibility with various ammunition types tailored to the smoothbore's strengths.

Ammunition types and examples

Common ammunition for smoothbores exploits either dispersal or alternative stabilization methods. Typical examples include:

  • Shot cartridges—many sporting and defensive shotguns fire multiple small pellets that create a widening pattern useful at close range.
  • Slugs—single, large projectiles designed for smooth barrels; some slugs are rifled internally or used with special chokes to improve stability.
  • Fin-stabilized and sabot rounds—used in some tank guns and artillery to deliver high-velocity, single-projectile performance without rifling.
  • Mortar and smoothbore cannon rounds—often designed for indirect fire and area effect rather than pinpoint long-range accuracy; see general artillery types at mortars and artillery.

History and development

Smoothbore weapons are among the oldest firearms technologies. Early muskets and cannon were smoothbore because rifling came later and was harder to produce consistently. During the 19th century, advances in rifling and ammunition improved long-range accuracy and led to widespread adoption of rifled small arms and field guns. Despite that shift, smoothbores retained important roles where their particular characteristics were advantageous—most notably in shotguns for hunting and sport, in certain artillery classes, and in some military applications.

Uses, advantages and distinctions

Today smoothbores remain important where their trade-offs are useful. Shotguns (the plurality of which are smoothbore designs) are prized for close-range effectiveness and the ability to use a variety of loads. Mortars and many large-caliber infantry support weapons favor simple, robust smoothbore barrels for indirect fire. In armored warfare, several modern tank guns are built as smoothbores so they can fire very-high-velocity, fin-stabilized kinetic rounds (using sabots) as well as versatile explosive projectiles.

In short, a smoothbore is not inherently inferior or superior to a rifled barrel; it is a different engineering choice optimized for particular kinds of ammunition, tactical roles, and manufacturing considerations.