How did WW II era tracer bullets light up?

The tracer ammo has an extra addition to it to allow the projectile to trace. Some people think that they are in the point of the ammo but that is not true. The tracer is actually in the base of the ammo. It has a compound that is made from strontium - magnesium and when it is used it will give off a red glow. The other thing that is amazing about these rounds is that they also have a delay. This is an important part of the use so that the position of the shooter is not given away. The shooter needs to be able to see where their shots are landing but they do not want an enemy to know exactly where they are. The delay allows them to have this option.