No, a katana or any traditional sword is not capable of effectively stopping or blocking bullets. The speed, force, and penetration power of bullets fired from firearms far exceed the resistance and durability of a sword blade.

Bullets travel at high velocities and are specifically designed to penetrate targets. When a bullet impacts a solid object, it can easily penetrate or pass through it, including metal, wood, or other materials. The blade of a katana, while sharp and strong, is not designed to withstand or redirect the impact of bullets.

Attempting to block or stop a bullet with a katana would be extremely dangerous and ineffective. The bullet's momentum and kinetic energy would likely overcome the strength of the blade, potentially causing severe injury or death to the wielder.

When it comes to dealing with firearms and bullets, it is important to prioritize personal safety and seek appropriate modern self-defense measures or take cover if faced with a threatening situation involving firearms. Firearms and bullet-resistant materials are specifically designed to provide protection against bullets, whereas traditional swords are not.

Always prioritize safety and follow the laws and regulations of your jurisdiction when considering self-defense options.