Why are there circles of spirals in the gun barrel?

When guns were first invented, the barrel and the inside of the barrel were smooth, without spirals. At that time, after the bullets and cannonballs were fired, they kept running straight forward, but the hit rate was too low. In the past, there were some jokes before the battle between the two armies. Sometimes the bullets and artillery shells just flew a short distance before they somersaulted and fell. There were also bullets and artillery shells that just turned around and ran towards their own position as soon as they came out of the muzzle of the gun. Even though it was only later, the reason was finally found. The problem is that when the bullets and cannonballs are flying, they always stagger around, are not stable enough, and even somersault due to the resistance of the air in the air. It was the top that the children played with that solved this problem. People were inspired by tops, and some suggested carving circles of spirals on the inner walls of gun barrels and cannon barrels. In this way, when the bullets and cannonballs are fired along this spiral, they will rotate around their own axis at high speed like a top. If any object rotates around itself, the direction of the axis of rotation will remain unchanged due to the inertia of rotation. In this way, it is like a top and will not tilt around. After the bullets and cannonballs are fired, since they are spinning forward like Tuolai, their bodies will not tilt around, and the warheads will always point towards the target. Even if they encounter air currents, they will not change directions easily. This greatly improves the hit rate. The faster the top spins, the less likely it is to fall over. When bullets and cannonballs fly, the faster they spin, the more stable their direction is. Therefore, most modern rifle barrels are engraved with four spiral lines. When the bullet comes out of the muzzle, it can rotate 3,600 times per second!