Patent Arms produced smoothbore revolving carbines and shotguns. Rarer were the drillings that used two rifled barrels and a single smoothbore barrel. Operators may fire spin-stabilized rounds from either a smoothbore or a rifled barrel. In appearance, the rifle musket was similar to the smoothbore musket. This practice was especially prevalent with some of the older smoothbore muskets and converted flintlocks. The term was only used for weapons that directly replaced smoothbore muskets. Grom low-pressure smoothbore cannon. Projectiles in smoothbore firearms are quite loose in the barrel. However, the new turret is necessary if a smoothbore gun is selected. For a smoothbore, the projectile was a round "cannonball". IZh-43 is a side by side smoothbore shotgun. IZh-58 is a side by side smoothbore shotgun. Freebore is a groove-diameter length of smoothbore barrel without lands forward of the throat. "Grom" low pressure smoothbore semi-automatic gun. Some smoothbore firearms are still used.