7.62 x 39mm API bullets

What exactly causes the incendiary compound in typical 7.62 x 39mm API bullets to ignite? Looking at pictures of sectioned bullets it appears that the AP core fully occupies the front 80% of the bullet while the incendiary compound sits directly behind the core at the base of the bullet. This seems a little odd to me, if the AP core passes straight through the target then surely the incendiary compound will just follow it through? Is it burning when it leaves the weapon - which presumably would give a tracer effect - or does it ignite on impact with the target? But how?

Jim, target ballistics can be complicated sometimes.
The incendiary in the back can be ignited by several factors. Some are (sure there are more):

  • upon impact on a hard surface the jacket keeps it’s momentum and moves on forward onto the core’s backside and is compressing the compound and sowith igniting it (pressure generates heat)
  • upon impact the core penetrates hard target material and keeps moving through it, the compound behind the core comes loose and follows the core which by penetrating the target material heated up the surface of it and the compound gets ignited this way

Ignition upon firing is no option here.

Okay, thanks Alex.