膛线（阴线及阳线）

膛线由加工在枪管内部膛孔中的螺旋形凹槽（阴线）和凸起表面（阳线）组成。该部件使弹丸在通过枪管时产生旋转运动，通过陀螺效应稳定其飞行。缠距（完成一次完整旋转的距离）根据弹丸质量、速度和预期用途精确设计。

膛线的螺旋几何形状在弹丸在气体压力下向前运动时与弹丸接合（通常通过嵌入软金属被甲或直接接触弹丸的承压面）。这将线性动能转化为角动量，产生陀螺稳定性，抵消偏航和进动，确保弹丸保持其预期弹道。

The rifling's helical geometry engages the projectile (typically via engraving into a soft metal jacket or direct contact with the bullet's bearing surface) as it moves forward under gas pressure. This converts linear kinetic energy into angular momentum, creating gyroscopic stability that counters yaw and precession, ensuring the projectile maintains its intended trajectory.