Smoothbore A smoothbore weapon is one which has a barrel without rifling . Smoothbores range from handheld firearms to powerful tank gun s and large artillery mortar s . History of firearms and rifling . Early firearms had smooth barrels , and fired projectiles with no significant spin . These projectiles had to have stable shapes , such as finned arrows or sphere s , to minimize tumbling during flight . However , spherical bullet s do tend to rotate randomly during flight , and the Magnus effect means that even a relatively smooth sphere will curve when rotating on any axis not parallel to the direction of travel ( see knuckleball for an example of intentional random tumbling . ) A rifled barrel , having spiral grooves or polygonal rifling , imparts a gyroscopic spin to the projectile that stabilizes it in flight and prevents it from tumbling . This does two things ; first , it increases the accuracy of the projectile by eliminating the random drift due to the Magnus effect , and second , it allows a longer , heavier bullet to be fired from the same caliber barrel , increasing range and power ( see external ballistics ) . In the eighteenth century , the standard infantry arm was the smoothbore musket ; by the nineteenth century , rifled barrels became the norm , increasing the power and range of the infantry weapon significantly . Modern smoothbores . Some smoothbore firearms are still used . Small arms . A shotgun fires multiple , round shot ; firing out of a rifled barrel would impart centrifugal force s that result a doughnut - shaped pattern of shot ( with a high projectile density on the periphery , and a low projectile density in the interior ) . While this may be acceptable at close ranges ( some spreader choke s are rifled to produce wide patterns at close range ) this is not desirable at longer ranges , where a tight , consistent pattern is required to improve accuracy . Another smoothbore weapon in use today is the 37 - mm riot gun , that fires non - lethal munitions like rubber bullet s and teargas at short range at groups of people , where a high degree of accuracy is not required . Artillery . The cannon made the transition from smoothbore firing cannonballs to rifled firing shells in the 19th century . However in more recent times , tank gun s have moved back to smoothbore . To reliably penetrate the thick armor of modern armored vehicles , a very long , thin kinetic - energy projectile is required . The longer the projectile is in relation to its diameter , the higher the spin rate must be to provide stability . Practical rifling can only stabilize projectiles of a limited length - to - diameter ratio , and these modern rounds are simply too long . These rounds are instead formed into a dart shape , using fins for stabilization . With the fins for stability , rifling is no longer needed , and in fact the spin imparted by rifling would degrade the accuracy of a finned projectile . The first tank with a smoothbore gun was the Soviet T - 62 , introduced into service in 1961 ; today all main battle tanks except the British Challenger 2 and Indian Arjun MBT use smoothbore guns . The Russia n navy conducted experiments with large - caliber smoothbore naval guns , which were halted by budget cuts . The armour - piercing gun evolution has also shown up in small arms , particularly the now abandoned U . S . Advanced Combat Rifle ( ACR ) program . The ACR " rifles " used smoothbore barrels to fire single or multiple flechette s ( tiny darts ) , rather than bullets , per pull of the trigger , to provide long range , flat trajectory , and armor - piercing abilities . Just like kinetic - energy tank rounds , flechettes are too long and thin to be stabilized by rifling and perform best from a smoothbore barrel . The ACR program was abandoned due to reliability problems and poor terminal ballistics . Mortar barrels are typically muzzle - loading smoothbores . Since mortars fire bombs which are dropped down the barrel and must not be a tight fit , a smooth barrel is essential . The bombs are fin - stabilized .