How does a rifle primer work? What happends imediately after the primer is struck, but beofre getting to the gun powder?

Primers in center-fire cartridges are little metallic capsules that contain explosive compounds that are highly sensitive to impact, most commonly lead azide. When the firing pin strikes the capsule, the capsule is indented and the crystals of the compound are crushed, causing them to explode. This sends a tongue of flame shooting forward into the powder contained in the cartridge casing,