弹 has two pronunciations, and there are many words composed of 弹. If you remember the pronunciation for everyone of these words, huh, it’s really a tough job. Don’t you like a shortcut that can make it easier to learn this word? Yes, there is one:
Keep the following rule in mind:
When 弹 expresses weapons e.g. 子弹，弹药，导弹，弹头, etc, 弹 is pronunced dàn, in other cases, it is prounced tán.