Precise machining of the muzzle is crucial to accuracy, because it is the last point of contact between the barrel and the projectile. If gaps exist between the muzzle and the projectile, escaping propellant gases may spread unevenly and deflect the projectile from its intended path (see transitional ballistics). In the case of rifled weapons, the contour of a muzzle is designed to keep the rifling safe from damage, so it is commonly recessed or protected by a convex "crown".