Why do you hear 2 different younds when an A-10 Warthog fires?

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Is it the sound of the powder exploding then the bullet breaking the sound barrier? Is one of them the projectile itself impacting/exploding?

For clarity, I mean it like [this](https://youtu.be/FVQvH4qc5cg?t=22). What is the first, sharper sound, and what is the secind, softer sound?

In: Physics