Rifled barrel
A rifled barrel was a firearm  with internal surface spiral grooves that allowed a projectile to be shot further and straighter than barrels without rifling.

In 2267, the Klingon Empire contacted the natives of Neural and began giving them weapons such as flintlock rifles. In 2268, the Klingon  told the Neural native Apella that he would give him improvements to his rifles, specifically a rifled barrel. ()

External link 
 

Weapon components